#include <iostream>
using namespace std;

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

	cin >> A;
	if (0 <= A && A <= 8) {
		X = 2;
	} else {
		for (int i = 2; A >= i * 1 + 7; i++) {
			if (A == 7 + i * 1) {
				X = i;
				break;
			}
		}
	}

	cout << X << endl;
	return 0;
}