import java.io.*;
import java.util.Scanner;

class Main {

    public static void main(String[] args) throws IOException {

        Scanner reader = new Scanner(new FileInputStream("fact.in"));

        int p = reader.nextInt();
        int step = 1;

        while (p > 0) {
            if (step % 5 == 0) p -= 2;
            else p -= 1;
            step += 1;
        }

        BufferedWriter writer = new BufferedWriter(new FileWriter("fact.out"));
        writer.write(String.valueOf(step));
        writer.close();
        reader.close();
    }

}