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::*;

fn main() {
    let a = read();
    let b = read();
    let h = read();

    println!("{}", (a + b) * h / 2);
}

fn read() -> usize {
    let s = stdin();
    let b = s.bytes()
        .map(|c| c.unwrap() as char)
        .take_while(|c| !c.is_whitespace())
        .collect::<String>();
    b.parse::<usize>().ok().unwrap()
}

//fn read_vec() -> Vec<char> {
//    let mut s = String::new();
//    stdin().read_line(&mut s).expect("poi");
//    s.chars().collect()
//}