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