Problem:
Score : 100 points

Problem Statement

There are N children in AtCoder Kindergarten. Mr. Evi will arrange the children in a line, then give 1 candy to the first child in the line, 2 candies to the second child, ..., N candies to the N-th child. How many candies will be necessary in total?

Constraints

1≦N≦100

Input

The input is given from Standard Input in the following format:

N

Output

Print the necessary number of candies in total.

Sample Input 1

3

Sample Output 1

6

The answer is 1+2+3=6.

Sample Input 2

10

Sample Output 2

55

The sum of the integers from 1 to 10 is 55.

Sample Input 3

1

Sample Output 3

1

Only one child. The answer is 1 in this case.

Solution in Rust (1.15.1) (judge verdict: Accepted)

use std::error::Error;
use std::io::{BufReader, Read};

const P: u32 = 1000000007;

fn main() {
    let mut s = String::new();
    let mut stdin = std::io::stdin();
    stdin.read_line(&mut s);
    let n: u32 = s.trim().parse().unwrap();
    println!("{}", n * (n + 1) >> 1);
}