import java.util.Scanner;

public class AmrAndPins {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int r = sc.nextInt(), x = sc.nextInt(), y = sc.nextInt(), x1 = sc.nextInt(), y1 = sc.nextInt();
        int dx = x1 - x;
        int dy = y1 - y;
        System.out.println(Math.max(0, (int)Math.ceil(Math.sqrt(dx * dx + dy * dy) / (2 * r))));
    }
}
