import java.util.*;
public class CF507B {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int r = in.nextInt();
		int x1 = in.nextInt();
		int y1 = in.nextInt();
		int x2 = in.nextInt();
		int y2 = in.nextInt();
		
		double dist =Math.sqrt((x1 - x2)*(x1 - x2) + (y1 - y2)*(y1 - y2));
		r = 2*r;
		
		int c = (int)(dist/r) + (dist%r < 1e-9? 0 : 1);
		System.out.println(c);
	}
}
