using System;

public class Program

{

    public static void Main()

    {

        double a = int.Parse(Console.ReadLine());

        double b = int.Parse(Console.ReadLine());

        double h = int.Parse(Console.ReadLine());

        double sum = (a + b) * h /2;

        Console.WriteLine("({0}+{1}) * {2} /2 = {3}", a, b, h, sum);

    }

}