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

/**************************************************************
	Problem: 2340
	User: huangsheng
	Language: C++
	Result: Accepted
	Time:49 ms
	Memory:2072 kb
****************************************************************/