using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace InstrukcjeWarunkowe05
{
    class Program
    {
        static double Funkcja1(int a, int b, int c)
        {
            if (a<=0 || b<=0 || c<=0)
            {
                return -1;
            }
           return (a+2.0*b-5.0*c) / (a * c);
        }

        static void Main(string[] args)
        {
            Console.WriteLine(Funkcja1(1,2,5));
            Console.ReadKey();
        }
    }
}