#include<bits/stdc++.h>
using namespace std;
int ans;
int main(){
    int n;
    cin>>n;
    for(int i=1;i<=n;i++){
        ans+=i;
    }
    cout<<ans;
	return 0;
}
/**************************************************************
	Problem: 1002
	User: linyifan
	Language: C++
	Result: Accepted
	Time:15 ms
	Memory:2072 kb
****************************************************************/