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>
#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define pop pop_back()
#define sz size()
using namespace std;
typedef long long ll;
bool isPrime(ll n)
{
    if(n==1)
        return false;
    for(ll i=2;i*i<=n;i++)
        if(n%i==0)
        return false;
    return true;
}
int lcm(ll a, ll b)
{
    ll temp = __gcd(a, b);

    return temp ? (a / temp * b) : 0;
}
unordered_map<ll,ll>mapp;
ll ma=-999;
///////////////////////////////////////////
ll n,m,i,j,in=-1,cnt,sum;
vector<ll>vi;
string s;
long double r;
long double mi=100000000;
ll a[200000],c,x,y;
int main(){
    cin>>n;
    cout<<n*(n+1)/2;
}