#include <iostream>

using namespace std;

int main()
{
    int n;
    cin >> n;
    int cnt[100] = {0};
    int a;
    for (int i = 0; i < n; i++) {
        cin >> a;
        cnt[a]++;
    }
    int tans = cnt[1] + cnt[2];
    int ans = tans;
    for (int i = 2; i < 99; i++) {
        tans = tans - cnt[i - 1] + cnt[i + 1];
        if (ans < tans) ans = tans;
    }
    cout << ans << endl;
    return 0;
}