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 <string>
#include <algorithm>
#define For(i, n) for(int i = 0; i < (n); i ++)
#define Range(c) c.begin(), c.end()
#define RevRange(c) c.begin(), c.end()
#define Cin(T, x) T x; cin >> x;
#define Cins(T, n, xs) vector<T> xs(n); For(i, n) cin >> xs[i];
#define Cout(val) cout << (val) << "\n";
#define Sort(a) sort(Range(a));
#define DeSort(a) sort(RevRange(a));

using namespace std;
using ll = long long;

int main(void){
    Cin(int, a);
    Cin(int, b);
    Cin(int, c);
    Cin(int, d);
    Cout(a*(a+1)/2);
    //Cout(() ? "Yes" : "No");
    //Cout(() ? "YES" : "NO");
}