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++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <iostream>
#include <vector>
#include <map>
#include <algorithm>
#include <string>
#include <cmath>
#include <stack>
#include <queue>
#include <list>
#include <set>
using namespace std;
#define rep(i, n) for(int i = 0; i < n; i++)
#define all(x) (x).begin(), (x).end()
#define INF 1010101010
#define MOD 1000000007
#define LL long long
using Coord = pair<int, int>;

int main() {
    int n;
    cin >> n;

    cout << (n + 1) * n / 2 << endl;
}