#include <bits/stdc++.h> #define rep(i,n)for(int i=0;i<(n);i++) #define MOD 1000000007 #define INF 0x3f3f3f3f #define INFL 0x3f3f3f3f3f3f3f3f #define EPS (1e-10) using namespace std; typedef long long ll; typedef pair<int,int>P; signed main(){ int a;cin>>a; if(a>=15){ cout<<a-7<<endl; } else cout<<-1<<endl; }