import java.util.Scanner;
public class LabProgram {
// Method to convert feet to steps
public static int feetToSteps(double userFeet) {
return (int)(userFeet / 2.5);
}
public static void main(String[] args) {
Scanner scnr = new Scanner(System.in);
double userFeet = scnr.nextDouble();
int steps = feetToSteps(userFeet);
System.out.println(steps);
}
}