import java.util.Scanner;


public class AmeAndPin {

	public static void main(String[] args) {
		// TODO Auto-generated method stub

		Scanner in=new Scanner(System.in);
		double r=in.nextDouble();
		double x1=in.nextDouble();
		double y1=in.nextDouble();
		double x2=in.nextDouble();
		double y2=in.nextDouble();
		double xx=(x2-x1)*(x2-x1);
		//System.out.println(xx);
		double yy=(y2-y1)*(y2-y1);
		//System.out.println(yy);
		double dis=(double)Math.sqrt(xx+yy);
		//System.out.println(dis);
		int num=(int) Math.ceil((Math.ceil(dis)/(2*r)));
		System.out.println(num);
	}

}
