import java.util.*;
public class Amr_and_Pins{
	public static void main(String[] args) {
		Scanner in =  new Scanner(System.in);
		int r = in.nextInt();
		int x1  = in.nextInt(),y1  = in.nextInt(),x2  = in.nextInt(),y2  = in.nextInt(); 
		double k = Math.sqrt(Math.pow(x2-x1,2)+Math.pow(y2-y1,2))/(2*r);
		int ans = (int)Math.ceil(k);
		System.out.println(ans);
	}
}