import java.util.Scanner;
import java.util.*;
public class A490 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
         Scanner s = new Scanner(System.in);
        int r = s.nextInt();
        int x = s.nextInt();
        int y = s.nextInt();
        int x1 = s.nextInt();
        int y1 = s.nextInt();
        double r1 = Math.sqrt(Math.pow(x-x1,2)+Math.pow(y-y1,2))-r;
        if(x==x1 && y==y1){
            System.out.println(0);
            return;
            
        }
        if(r1<r){
            System.out.println(1);
            return;
        }
        if(r1/r==0){
            System.out.println(1);
        }else{
            if(r1%r==0){
                System.out.println((int)(r1/r));
            }else{
                System.out.println((int)r1/r);
            }
        }
         
	}

}