#include <bits/stdc++.h>
using namespace std;
const int N = 111;
int n, a[N] = {0};

int main() {
    cin >> n;
    for (int i = 1; i <= n; i++) {
        int x; cin >> x;
        a[x]++;
    }
    int res = 2;
    for (int i = 1; i < 100; i++) res = max(res, a[i] + a[i + 1]);
    cout << res << endl;
}