//package contest_23_01_2015;


import java.util.Scanner;


public class B {

public static void main(String[] args) {
	Scanner sc=new Scanner(System.in);
	
	double r=sc.nextDouble();
	
	double xa=sc.nextDouble();
	
	double ya=sc.nextDouble();
	
	double xxa=sc.nextDouble();
	
	double yya=sc.nextDouble();
	
	double l=Math.sqrt((xxa-xa)*(xxa-xa)+(yya-ya)*(yya-ya));
	
	if(l%(2*r)==0){
		System.out.println((int)(l/(2*r)));
	
	}else{
		System.out.println((int)(l/(2*r)+1));
	}
}
}
