import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) throws IOException{
        // TODO code application logic here
        InputReader ir = new InputReader();
        int n = ir.readInt(),a[];
        a = ir.readIntArray(n);
        int no[] = new int[101];
        for(int i=0;i<n;i++){
            no[a[i]]++;
        }
        int ans = 2;
        for(int i=1;i<=100;i++){
//            System.out.println(i+" "+no[i]);
                ans = Math.max(ans, no[i]+no[i-1]);
            
        }
        System.out.println(ans);
        
    }
    final static class InputReader {
        //This IO class belongs to Ashok Rajpurohit (@ashok1113)
        byte[] buffer = new byte[8192];
        int offset = 0;
        int bufferSize = 0;
        final InputStream in = System.in;

        public int readInt() throws IOException {
            int number = 0;
            int s = 1;
            if (offset == bufferSize) {
                offset = 0;
                bufferSize = in.read(buffer);
            }
            if (bufferSize == -1) {
                throw new IOException("No new bytes");
            }
            for (; buffer[offset] < 0x30 || buffer[offset] == '-'; ++offset) {
                if (buffer[offset] == '-') {
                    s = -1;
                }
                if (offset == bufferSize - 1) {
                    offset = -1;
                    bufferSize = in.read(buffer);
                }
            }
            for (; offset < bufferSize && buffer[offset] > 0x2f; ++offset) {
                number = (number << 3) + (number << 1) + buffer[offset] - 0x30;
                if (offset == bufferSize - 1) {
                    offset = -1;
                    bufferSize = in.read(buffer);
                }
            }
            ++offset;
            return number * s;
        }

        public int[] readIntArray(int n) throws IOException {
            int[] ar = new int[n];
            for (int i = 0; i < n; i++) {
                ar[i] = readInt();
            }

            return ar;
        }

        public int[] readIntArray1(int n) throws IOException {
            int[] ar = new int[n + 1];
            for (int i = 1; i <= n; i++) {
                ar[i] = readInt();
            }

            return ar;
        }

        public long readLong() throws IOException {
            long res = 0;
            int s = 1;
            if (offset == bufferSize) {
                offset = 0;
                bufferSize = in.read(buffer);
            }
            for (; buffer[offset] < 0x30 || buffer[offset] == '-'; ++offset) {
                if (buffer[offset] == '-') {
                    s = -1;
                }
                if (offset == bufferSize - 1) {
                    offset = -1;
                    bufferSize = in.read(buffer);
                }
            }
            for (; offset < bufferSize && buffer[offset] > 0x2f; ++offset) {
                res = (res << 3) + (res << 1) + buffer[offset] - 0x30;
                if (offset == bufferSize - 1) {
                    offset = -1;
                    bufferSize = in.read(buffer);
                }
            }
            ++offset;
            if (s == -1) {
                res = -res;
            }
            return res;
        }

        public long[] readLongArray(int n) throws IOException {
            long[] ar = new long[n];

            for (int i = 0; i < n; i++) {
                ar[i] = readLong();
            }

            return ar;
        }

        public String read() throws IOException {
            StringBuilder sb = new StringBuilder();
            if (offset == bufferSize) {
                offset = 0;
                bufferSize = in.read(buffer);
            }

            if (bufferSize == -1 || bufferSize == 0) {
                throw new IOException("No new bytes");
            }

            for (;
                    buffer[offset] == ' ' || buffer[offset] == '\t' || buffer[offset]
                    == '\n' || buffer[offset] == '\r'; ++offset) {
                if (offset == bufferSize - 1) {
                    offset = -1;
                    bufferSize = in.read(buffer);
                }
            }
            for (; offset < bufferSize; ++offset) {
                if (buffer[offset] == ' ' || buffer[offset] == '\t'
                        || buffer[offset] == '\n' || buffer[offset] == '\r') {
                    break;
                }
                if (Character.isValidCodePoint(buffer[offset])) {
                    sb.appendCodePoint(buffer[offset]);
                }
                if (offset == bufferSize - 1) {
                    offset = -1;
                    bufferSize = in.read(buffer);
                }
            }
            return sb.toString();
        }

        public String read(int n) throws IOException {
            StringBuilder sb = new StringBuilder(n);
            if (offset == bufferSize) {
                offset = 0;
                bufferSize = in.read(buffer);
            }

            if (bufferSize == -1 || bufferSize == 0) {
                throw new IOException("No new bytes");
            }

            for (;
                    buffer[offset] == ' ' || buffer[offset] == '\t' || buffer[offset]
                    == '\n' || buffer[offset] == '\r'; ++offset) {
                if (offset == bufferSize - 1) {
                    offset = -1;
                    bufferSize = in.read(buffer);
                }
            }
            for (int i = 0; offset < bufferSize && i < n; ++offset) {
                if (buffer[offset] == ' ' || buffer[offset] == '\t'
                        || buffer[offset] == '\n' || buffer[offset] == '\r') {
                    break;
                }
                if (Character.isValidCodePoint(buffer[offset])) {
                    sb.appendCodePoint(buffer[offset]);
                }
                if (offset == bufferSize - 1) {
                    offset = -1;
                    bufferSize = in.read(buffer);
                }
            }
            return sb.toString();
        }
    }
}