#include<iostream>
using namespace std;
int N;
bool check(long T)
{
	return T*(T+1)/2>=N;
}
main()
{
	cin>>N;
	int L=0,R=N;
	while(R-L>1)
	{
		int mid=(L+R)/2;
		if(check(mid))R=mid;
		else L=mid;
	}
	cout<<R<<endl;
}