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 9.2.1) (judge verdict: Wrong Answer)

#include <stdio.h>

char s[100001];

int main(void)
{
	int n;
	char a, b, c;

	a = 0;
	b = 1;
	c = 2;

	scanf("%s", s);
	for (n = 0; s[n]; ++n)
	{
		a = s[n];
		if (a == b || a == c || b == c)
		{
			if (n < 2)
			{
				printf("1 2\n");
			}
			else
			{
				printf("%d %d\n", n - 1, n + 1);
			}
			return 0;
		}
		c = b;
		b = a;
	}

	printf("-1 -1\n");

	return 0;
}