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

class Program
{
	static void Main()
	{
		int n = int.Parse(Console.ReadLine()); //数字1つを読み込み

		int ans = n - 7;
		if (n < 2)
		{
			ans = -1;
		}

		Console.WriteLine(ans);
	}
}