#include<bits/stdc++.h>
using namespace std;
int main()
{
	int n=1,s=0;
	while(s<5000)
	{
		s=s+n;
		n=n+1;
	}
	cout<<s;
	return 0;
} 
/**************************************************************
	Problem: 1146
	User: wangyuxin
	Language: C++
	Result: Wrong Answer
****************************************************************/