#include <iostream>
#include <algorithm>

using namespace std;

int main() {
    std::ios::sync_with_stdio(false);
    
    int N;

    cin >> N;

    int A;
    int F[100];

    fill_n(F, 100, 0);

    for (int i = 0; i < N; i++) {
        cin >> A;
        F[A]++;
    }

    int cnt = 0;

    for (int i = 2; i < 100; i++) {
        cnt = max(cnt, F[i - 1] + F[i]);
    }

    cout << cnt << endl;
    
    return 0;
}