#include<iostream>
#include<cstdio>
#include<algorithm>
#include<vector>
#include<map>
#include<set>
#include<cstring>
#include<cstdlib>
#include<string>
#include<numeric>
using namespace std;

#define int long long
#define rep(i,n) for(int i=0;i<(n);i++)
#define all(v) (v).begin(),(v).end()
typedef vector<int>vint;
typedef pair<int,int>pint;
typedef vector<pint>vpint;
template<typename A,typename B>inline void chmin(A &a,B b){if(a>b)a=b;}
template<typename A,typename B>inline void chmax(A &a,B b){if(a<b)a=b;}


signed main(){
    int a;cin>>a;
    if(a<15){
        cout<<-1<<endl;
    }
    else{
        cout<<a-7<<endl;
    }
    return 0;
}