import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
public class Boj_2292 {
public static void main(String[] args) throws IOException {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
int inputNum = Integer.parseInt(br.readLine());
int j = 1;
int newI = 2;
while(newI <= inputNum) {
newI += 6 * j++;
}
System.out.println(j);
}
}