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 Rust (1.15.1) (judge verdict: Accepted)

use std::io::Read;

fn main() {
    let (a, b, h) = {
        let mut buf = String::new();
        std::io::stdin().read_to_string(&mut buf).unwrap();
        let mut iter = buf.split_whitespace();
        let a: usize = iter.next().unwrap().parse().unwrap();
        let b: usize = iter.next().unwrap().parse().unwrap();
        let h: usize = iter.next().unwrap().parse().unwrap();
        (a, b, h)
    };
    print!("{}", (a + b) * h / 2);
}