#include <bits/stdc++.h>
using namespace std;
int ss(int n){
	int r;
	if(n==1)
		r=1;
	else
		r=ss(n-1)+n-1;
	return r;
}
int main(){
	int i=1,s=0;
	while(s<5000){
		s=s+ss(i);
		i++;
	}
	cout<<s;
	return 0;
	}

/**************************************************************
	Problem: 1146
	User: fzy001
	Language: C++
	Result: Accepted
	Time:3 ms
	Memory:2072 kb
****************************************************************/