#include <iostream>
using namespace std;
int main(int argc, char* argv[])
{
	int A;
	cin>>A;
	if (A>7){
		int X=A-7;
		if (X<=7){
			cout<<-1<<endl;
		}else{
			cout<<A-7<<endl;
		}
	}else{
		cout<<-1<<endl;
	}
	return 0;
}