#include <map>
#include <set>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <queue>
#include <stack>
#include <string>
#include <bitset>
#include <cstdio>
#include <limits>
#include <vector>
#include <climits>
#include <cstring>
#include <cstdlib>
#include <fstream>
#include <numeric>
#include <sstream>
#include <iostream>
#include <algorithm>
#include <unordered_map>

using namespace std;


int main(){
    int n;
    cin >> n;
    vector<int> a(n);
    for(int a_i = 0;a_i < n;a_i++){
       cin >> a[a_i];
    }
    sort(a.begin(), a.end());
    int best = 0;
    int last = 0;
    int current = 0;
    int current_no = a[0];
    for (int i = 0;i < n;++i){
        if (a[i] != current_no) {
            if (a[i] == current_no + 1) last = current;
            else last = 0;
            current = 0;
            current_no = a[i];
        }
        ++current;
        if (current + last > best) best = (current + last); 
    }
    cout << best;
    return 0;
}