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) {
		// TODO Auto-generated method stub-
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt(), a[] = new int[n] ;
		for(int i=0; i<n; i++){
			a[i] = sc.nextInt();
		}
		Arrays.sort(a);
		ArrayList<Integer> max = new ArrayList<>();
		int last=-1;
		for(int i=0; i<a.length-1; i++){
			if(a[i+1]-a[i] <= 1){
				if(a[i+1]-last <= 1){
					max.set(max.size()-1, max.get(max.size()-1)+1);
				} else {
					last = a[i];
					while(i>=1 && a[i-1] == last){
						i--;
					}
					max.add(2);
				}
			}
		}
		Collections.sort(max);
		System.out.println(max.get(max.size()-1));
	}
}