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<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> P;
typedef pair<ll,ll> Pl;
#define all(a) (a).begin(),(a).end()
#define rep(i,n) repi(i,0,n)
#define repi(i,a,b) for(ll i=(a);i<(b);i++)
#define rrep(i,n) for(ll (i)=(n)-1;(i)>=0;i--)
#define SHOW(x) cout << #x << ": " << x << endl;
const ll INF=1e18,MOD = 1e9+7;
const int iINF = 1e9;
int main(){
    int n;
    cin>>n;
    cout<<(n+1)* n /2<<endl;

}