#include <stdio.h>
#include <algorithm>
#include <vector>
#include <deque>
#include <string>
#include <iostream>
using namespace std;
using ll = long long;

void solve();
int main() {
	solve();
#ifdef DBG
	while (true);
#endif
}


//395
void solve() {
	int A;
	scanf("%d", &A);

	if (A < 15)
		printf("%d\n", -1);
	else
		printf("%d\n", A - 7);
}