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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int a = Integer.parseInt(sc.next());
		int b = Integer.parseInt(sc.next());
		int c = Integer.parseInt(sc.next());
		//int n = Integer.parseInt(sc.next());
		//long res=n;
		//int l = Integer.parseInt(sc.next());
		//int sum=0;
		//String s = sc.next();
		//int a = Integer.parseInt(sc.next());
		//String t = sc.next();

		/*if(b>a/2.0) {
			System.out.println(a-b);
		}else {
			System.out.println(b-1);
		}*/
		System.out.println((a+b)*c/2);
	}
}