#include<iostream>
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<queue>
#include<vector>
#include<stack>
#include<map>
#include<set>
#include<cmath>
#include<cctype>
#include<ctime>
#define pi acos(-1.0)
using namespace std;
int main()
{
	int n;
	scanf("%d",&n);
	int sum=0;
	for(int i=1;i<=n;i++)
	{
		sum+=i;
	}
	printf("%d\n",sum);
	return 0;
}

如此 2017/8/6 9:31:04
