//Write an expression that calculates trapezoid's area by given sides a and b and height h.

using System;

class Trapezoids
{
    static void Main()
    {
        Console.Write("Enetr a: ");
        double a = double.Parse(Console.ReadLine());

        Console.Write("Enetr b: ");
        double b = double.Parse(Console.ReadLine());

        Console.Write("Enetr h: ");
        double h = double.Parse(Console.ReadLine());

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