#include <iostream>

using namespace std;

int main()
{
    int n; // kolku denovi trael strajkot
    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;
}