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::io;

fn read_line<T: std::str::FromStr>() -> Vec<T> {
    let mut s = String::new();
    io::stdin().read_line(&mut s).ok();
    s.trim()
        .split_whitespace()
        .map(|s| s.parse().ok().unwrap())
        .collect()
}

fn solve_a(n: usize) -> usize {
    n * (n + 1) / 2
}

fn main() {
    let input = read_line::<usize>()[0];
    println!("{}", solve_a(input));
}