import java.util.Scanner;

/**
 * Created by sidharth on 19/9/15.
 */
public class AmrAndPins {
    public static void main(String[] args){

        Scanner sc = new Scanner(System.in);

        int r = sc.nextInt();
        int x = sc.nextInt();
        int y = sc.nextInt();
        int a = sc.nextInt();
        int b = sc.nextInt();

        double xDist = (a - x) * (a - x);
        double yDist = (b - y) * (b - y);
        //System.out.println((xDist + yDist));
        double distance = Math.sqrt(xDist + yDist);

        System.out.println((int) Math.ceil(distance / 2 * r));


    }
}