#include <iostream>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <algorithm>
#include <iomanip>
#include <cassert>
using namespace std;

#define GET_ARG(a,b,c,F,...) F
#define REP3(i,s,e) for (i = s; i <= e; i++)
#define REP2(i,n) REP3 (i,0,(int)(n)-1)
#define REP(...) GET_ARG (__VA_ARGS__,REP3,REP2) (__VA_ARGS__)
#define RREP3(i,s,e) for (i = s; i >= e; i--)
#define RREP2(i,n) RREP3 (i,(int)(n)-1,0)
#define RREP(...) GET_ARG (__VA_ARGS__,RREP3,RREP2) (__VA_ARGS__)
#define DEBUG(x) cerr << #x ": " << x << endl

typedef long long ll;

constexpr int INF = 1e8;
constexpr int MOD = 1e9+7;
constexpr int ESP = 1e-9;
constexpr double PI = acos(-1);

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