#include <iostream>
using namespace std;

int main() {
    int n;
    cin >> n;

    if(n <= 15) {
        cout << 0 << endl;
    }
    else if(n >= 16 and n <= 20) {
        cout << 1 << endl;
    }
    else if(n >= 21 and n <= 25) {
        cout << 2 << endl;
    }
    else {
        cout << 3 << endl;
    }
    return 0;
}