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: Accepted)

#include <stdio.h>

int main() {
	
	int a, sum = 0;
	scanf("%d", &a);
	float var = 2;
	int sn = a / var * (2 * 1 + (a - 1) * 1);
	printf("%d\n", sn);
	
	return 0;
}