import java.util.*;
import java.io.*;
import java.math.*;

public class jeroen
{
	public static void main(String[] args) throws Exception
	{
		BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
		long n = Long.valueOf(in.readLine());
		long best = 1;
		while((best + 1) * (best + 2) / 2 <= n) best++;
		System.out.println(best);
	}
}