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 JavaScript (Node.js 12.16.1) (judge verdict: Accepted)

function Main(input) {
    var array = input.replace(/\r?\n+$/, '').split(/\r?\n/).map(Number);
    console.log((array[0] + array[1]) * array[2] / 2);
}

var character = "";
process.stdin.on('data', function(char){ character += char });
process.stdin.on('end', function(){ Main(character); });
process.on('SIGINT', function() { Main(character); process.exit(0); });