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 (Clang 3.8.0) (judge verdict: Accepted)

#include <map>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#define LL long long
using namespace std;
const int MAXN = 2e5+55;
int vis[MAXN];
int main()
{
   int n;
   cin>>n;
   cout<<1ll*n*(n+1)/2;
    return 0;
}