import java.util.Scanner;

public class AmrAndPins {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int d = scan.nextInt()*2;
		//System.out.println(dist(scan.nextInt(), scan.nextInt(), scan.nextInt(), scan.nextInt()));
		System.out.println((int)Math.ceil(dist(scan.nextInt(), scan.nextInt(), scan.nextInt(), scan.nextInt())*1.0/(d*1.0)));
	}
	public static double dist(int x1, int y1, int x2, int y2) {
		return Math.sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
	}
}