using System;
using System.Collections.Generic;
using System.Linq;

namespace yukicode {
    public class Program {
        public static int Solver(System.IO.TextReader reader) {
            var a = int.Parse( reader.ReadLine() );
            if (a < 15) return -1;
            else return a - 7;
        }

        private static void Main() {
            Console.WriteLine( Solver( Console.In ) );
        }
    }
}