import java.util.*;

public class B507 {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		double r = scan.nextInt(), x = scan.nextInt(), y = scan.nextInt(), x1 = scan.nextInt(), y1 = scan.nextInt();
		double d = Math.sqrt((x1 - x) * (x1 - x) + (y1 - y) * (y1 - y));
		double res = Math.ceil(d / (2 * r));

		System.out.println((int) res);

	}
}
