#include <bits/stdc++.h>
using namespace std;
int main(){
	int m;
	cin>>m; 
	bool ok=0; 
	int s1=0,s2=1;
	while(m>=s2){
	    int p=s2;
		for(int i=1;i<=s2;i++){
			s1+=s2;
			p++;
			if(p>=m){
				cout<<s1;
				ok=1;
				break;
			}
		}
		if(ok) break;
		s2++;
	}
	if(ok!=1) cout<<s1;
}