#include <iostream>
using namespace std;

int main(void) {
	int A, X = -1;

	cin >> A;
	for (int i = 0; 7 + i <= A; i++) {
		if (7 + i == A && i > 7) {
			X = i;
			break;
		}
	}
	cout << X << endl;
	return 0;
}