import java.util.Scanner;

public class HELLLLL {

	public static void main(String[] args) {
		long b,c,d,e,f = 0,g;
		float a;
		Scanner scan=new Scanner(System.in);
		a=scan.nextInt();	
		b=scan.nextInt();
		c=scan.nextInt();
		d=scan.nextInt();
		e=scan.nextInt();
		if((b==d)&&(c==e))
		System.out.println("0");
		else
			{f=(int) Math.ceil(Math.sqrt(((b-d)*(b-d))+((c-e)*(c-e))));
			//System.out.println(f);
			g=(int) Math.ceil((f-2*a)/(2*a));
			//System.out.println(g);
			System.out.println(++g);
			}
			
	}
	}