#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;

int main()
{
     int n;

     cin >> n; 

     int a[10001];

     for ( int i=0; i<n; i++ )
     {
	  cin >> a[i] ;
     }

     sort(a,a+n);

     int count=0,b=0;

     for ( int i=0; i<n-1; i++ )
     {
	  count=0;

	  for ( int j=i; j<n-1; j++ )
	  {
	       if ( (a[j+1] - a[j]) <= 1 && (a[j+1]-a[i]) <= 1 )
		    count++;
	       else
		    break;
	  }

	  if ( count > b )
	       b=count;
     }

     cout << max(b+1,2) << endl ;

     return 0;
}