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;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using static System.Console;
using static System.Math;
using static System.Array;
using static Read;

class Program
{
    public static void Main()
    {
        var a = Int();
        var b = Int();
        var h = Int();
        WriteLine($"{(a + b) * h / 2}");
    }
}

static class Read
{
    static Queue<string> queue = new Queue<string>();
    static void Enqueue()
    {
        ReadLine().Split(' ').ToList().ForEach(a => queue.Enqueue(a));
    }
    public static int Int()
    {
        if(queue.Count == 0)
            Enqueue();
        return int.Parse(queue.Dequeue());
    }
    public static long Long()
    {
        if(queue.Count == 0)
            Enqueue();
        return long.Parse(queue.Dequeue());
    }
    public static double Double()
    {
        if(queue.Count == 0)
            Enqueue();
        return double.Parse(queue.Dequeue());
    }
    public static string String()
    {
        if(queue.Count == 0)
            Enqueue();
        return queue.Dequeue();
    }
    public static int[] IntArray()
    {
        return ReadLine().Split(' ').Select(a => int.Parse(a)).ToArray();
    }
    public static long[] LongArray()
    {
        return ReadLine().Split(' ').Select(a => long.Parse(a)).ToArray();
    }
    public static double[] DoubleArray()
    {
        return ReadLine().Split(' ').Select(a => double.Parse(a)).ToArray();
    }
    public static string[] StringArray()
    {
        return ReadLine().Split(' ');
    }
}