View Code of Problem 30

#include<stdio.h>
#include<iostream>
#include<cstdlib>
#include<cstdio>
#include<cstring>
#include<string>
#include<algorithm>
#include<vector>
#include<cmath>
#include<stack>
#include<map>
#include<vector>
#include<cstdbool>
using namespace std;

int main()
{
	long long n;
	while(cin >> n){
	cout << (1 + n) * n / 2 << endl;
	}
	
	return 0;
}