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

public class Solution {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int[] a = new int[n];
        for(int a_i=0; a_i < n; a_i++){
            a[a_i] = in.nextInt();
        }
      
      compute(a);
    }
  
  public static void compute(int[] arr) {
    int[] counts = new int[100];
    for (int i = 0; i < arr.length; i++) {
      counts[arr[i]]++;
    }
    
    // Now we have frequency of each number in counts.
    // We are looking for the sum of the greatest set of three.
    
    int max = Integer.MIN_VALUE;
    int tripletStartIdx = 0;
    
    for (int i = 0; i < counts.length - 1; i++) {
      int sum = counts[i] + counts[i + 1];
     // System.out.println("considering i: "+ i);
     // System.out.println("sum: "+ sum);
      if (sum > max) {
        max = sum;
        tripletStartIdx = i;
      }
    }
    
    System.out.println(max);
  }
}