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 scanner::Scanner;

fn main() {
    let mut sc = Scanner::new();
    let a: usize = sc.read();
    let b: usize = sc.read();
    let h: usize = sc.read();
    println!("{}", ((a + b) * h) / 2)
}

mod scanner {
    pub struct Scanner<'a> {
        s: String,
        words: ::std::str::SplitWhitespace<'a>,
    }

    impl<'a> Scanner<'a> {
        pub fn new() -> Scanner<'a> {
            let s = String::new();
            let words = unsafe { ::std::mem::transmute(s.split_whitespace()) };
            Scanner { s: s, words: words }
        }

        pub fn read<T: ::std::str::FromStr>(&mut self) -> T {
            match self.words.next() {
                Some(x) => x.parse().ok().unwrap(),
                None => {
                    self.load();
                    self.read()
                }
            }
        }

        fn load(&mut self) {
            self.s.clear();
            ::std::io::stdin().read_line(&mut self.s).unwrap();
            self.words = unsafe { ::std::mem::transmute(self.s.split_whitespace()) };
        }
    }
}