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 C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
class A
{
    static void Main()
    {
        string a = "";
        string s = Console.ReadLine();
        for (int i = 0; i < s.Length; i++)
        {
            string y = s.Substring(i, 1);
            if (y != "B") { a += y; }
            else { if (a != "") { a=s.Substring(0,a.Length -1 ); } }
        }
        Console.WriteLine(a);
    }
}