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


int main() 
{
    int n;
    cin >> n;
    int a[n];
    for(int i = 0; i < n; i++)
    {
        cin >> a[i];    
    }
    
    sort(a, a+n);
    int pc = 0, c = 0, mc = 0;
    for(int i = 0; i < n; i++)
    {
        int start = i;
        c = 1;
        //cout << start << " " << a[start] << endl;
        for(; (i < n-1) && (a[i] == a[i+1]); i++, c++);
        //cout << i << " " << a[i] << " " << c << " " << pc << endl;
        if(start > 0 && a[start] == a[start -1] + 1)
        {
            mc = max(mc, c + pc);    
        }
        else
        {
            mc = max(mc, c);    
        }
        pc = c;
    }
    
    cout << mc << endl;
    return 0;
}