#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;
}