import java.io.*;
import java.util.*;
import java.util.stream.*;

class Process {
    private long n;

    Process(long n) {
        this.n = n;
    }

    long getResult() {
        return (long)Math.sqrt(n / 3.0);
    }
}

public class Main {
    public static void main(String[] args) throws IOException {
        var bufferedReader = new BufferedReader(new InputStreamReader(System.in));
        var printWriter    = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));

        // 入力
        long n = Long.parseLong(bufferedReader.readLine().trim());

        // 処理および出力
        printWriter.println((new Process(n)).getResult());

        bufferedReader.close();
        printWriter.close();
    }
}