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>

int main(void){
    char s[12],buf[12];
    scanf("%s",s);
    //cntは現時点でのbuf内の要素数
    int i,cnt=0;
    for(i=0;i<strlen(s);i++){
        if(s[i]=='0'){
            buf[cnt]='0';
            cnt++;
        }else if(s[i]=='1'){
            buf[cnt]='1';
            cnt++;}
        else if(cnt>0){
            buf[cnt-1]=0;
            cnt--;
        }
    }
    printf("%s\n",buf);
}