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: Wrong Answer)

fn main() {
    let mut line = String::new();
    std::io::stdin().read_line(&mut line).unwrap();
    let mut v = Vec::new();

    for char in line.trim().chars() {
        match char {
            'B' => { v.pop(); },
            c if c == '0' || c == '1' => { v.push(c); },
            _ => () 
        }
    }

    let s = v
        .iter()
        .map(|s| s.to_string())
        .collect::<String>();

    println!("{}", s);
}