import java.util.Scanner;
public class Stick {
	public static void main(String args[]) {
		int r,x1,y1,x2,y2;
		Scanner input = new Scanner(System.in);
		r = input.nextInt();
		x1 = input.nextInt();
		y1 = input.nextInt();
		x2 = input.nextInt();
		y2 = input.nextInt();
		double dist = Math.sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1));
		System.out.print(Math.ceil(dist / (2.0 * r)));
	}
}