Problem:
Score : 100 points

Problem Statement

You are given a trapezoid. The lengths of its upper base, lower base, and height are a, b, and h, respectively.

An example of a trapezoid

Find the area of this trapezoid.

Constraints

1≦a≦100

1≦b≦100

1≦h≦100

All input values are integers.

h is even.

Input

The input is given from Standard Input in the following format:

a
b
h

Output

Print the area of the given trapezoid. It is guaranteed that the area is an integer.

Sample Input 1

3
4
2

Sample Output 1

7

When the lengths of the upper base, lower base, and height are 3, 4, and 2, respectively, the area of the trapezoid is (3+4)×2/2 = 7.

Sample Input 2

4
4
4

Sample Output 2

16

In this case, a parallelogram is given, which is also a trapezoid.

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;

class quiz
{
    public int solve(int a, int b, int h)
    {
        return (a + b) * h / 2;
    }

    public int[] ParseIntBySpace(string str)
    {
        int[] array = new int[str.Length];
        int lastloc = 0, spaceloc = -1;

        for (int i = 0; i < str.Length; i++)
        {
            if (str[i] == ' ')
            {
                array[lastloc++] = int.Parse(str.Substring(spaceloc + 1, i - spaceloc - 1));
                spaceloc = i;
            }
            else if (i == str.Length - 1)
            {
                array[lastloc++] = int.Parse(str.Substring(spaceloc + 1, i - spaceloc));
            }
        }

        Array.Resize(ref array, lastloc);

        return array;
    }
}

class Example
{
    static void Main()
    {
        quiz ex = new quiz();

        //while (true)
        //{
            Console.WriteLine(ex.solve(int.Parse(Console.ReadLine()), int.Parse(Console.ReadLine()),int.Parse(Console.ReadLine())));
        //}
    }
}