#include <iostream>
#define ll long long
using namespace std;
ll n, cc;
ll g(ll m, ll cnt){
	return m >= 0 ? cnt : -1;
}
int main() {
	cin >> n;
	while (n % 5){
		n -= 3;
		cc++;
	} 
	cout << g(n, cc);
	return 0;
}