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

/**************************************************************
	Problem: 2340
	User: linyifan
	Language: C++
	Result: Accepted
	Time:51 ms
	Memory:2072 kb
****************************************************************/