using System;

public class Program

{

    public static void Main()

    {

        int R1 ,R2 ,R3, RT;

        Console.WriteLine("R1=");

       R1= int .Parse(Console.ReadLine());

        Console.WriteLine("R2=");

       R2= int .Parse(Console.ReadLine());

        Console.WriteLine("R3=");

       R3= int .Parse(Console.ReadLine());

       RT= 1/(1/R1)+(1/R2)+(1/R3);

        Console.WriteLine("RT="+RT);

    }

}