#include<bits/stdc++.h>
using namespace std;
int main(){
    int n,ans=0;
    cin>>n;
    for(int i=1;i<=n;i++) ans+=i;
    cout<<ans;
 
    return 0;
}
/**************************************************************
	Problem: 1002
	User: zhengyuxuan
	Language: C++
	Result: Accepted
	Time:14 ms
	Memory:2072 kb
****************************************************************/