import java.io.PrintStream;

public class SumLessThanM
{
   public static void main(String[] args)
   {
      PrintStream out = System.out;
      
      final int N = Integer.parseInt(args[0]);
      int sum = 0;
      int count = 1;

      while (sum <= N)
      {
         sum += count;
         count++;
      }
      out.println(count - 1);
   }
}