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 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <stdio.h>
#include <string.h>

int main(void)
{
    char s[11], ans[11];
    int i;
    scanf("%s", s);
    for (i = 0; i < strlen(s); i++)
    {
        if (s[i] == '0') {
            ans[strlen(ans)] = '0';
        } else if (s[i] == '1') {
            ans[strlen(ans)] = '1';
        } else if (s[i] == 'B') {
            if (strlen(ans) != 0) {
                ans[strlen(ans) - 1] = '\0';
            }
        }
    }
    printf("%s\n", ans);
    return 0;
}