import java.util.Scanner;


public class CF507B {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int r = in.nextInt();
		long dx = in.nextInt();
		long dy = in.nextInt();
		dx -= in.nextInt();
		dy -= in.nextInt();
		int dist = (int)Math.ceil(Math.sqrt(dx*dx+dy*dy)/(2*r));
		System.out.println(dist);
	}

}