#include <iostream>
#include <vector>
#include <algorithm>
#include <string>

using namespace std;


void solve()
{
    int A;
    cin >> A;
    
    int ans = -1;
    
    for( int base=8; base<A; base++ )
    {
        if( base+7 == A )
        {
            ans = base;
            break;
        }
    }
    cout << ans <<endl;
}

int main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    solve();
    return 0;
}