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


int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
    int n;
    cin >> n;
    map<int,int> m;
    for(int i = 0;i < n;++i){
        int t;
        cin >> t;
        ++m[t];
    }
    int _max = 0;
    for(auto &p : m){
        int a = p.second;
        if(m.find(p.first+1) != m.end())
            a+=m[p.first+1];
        
        _max = max(a,_max);
    }
    cout << _max << endl;
    return 0;
}