#include <bits/stdc++.h>
using namespace std;
int main(){
	int n=0,ans=0;
	cin>>n;
	for(int i=1;i<=n;i++) ans+=i; 
	cout<<ans;
return 0;
}


/**************************************************************
	Problem: 1002
	User: linzihao
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/