#include<bits/stdc++.h>
using namespace std;
int n,sum;
int main(){
	cin>>n;
	int i=n;
	while(i>=1){
		sum+=i;
		i--;
	}
	cout<<sum;
	return 0;
}
/**************************************************************
	Problem: 1002
	User: zhangziang
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/