import java.util.*;
import java.lang.*;

public class Main 
{
	public static void main(String[]args) 
	{
		Scanner sc = new Scanner(System.in);
        double r=sc.nextInt();
        double x=sc.nextInt();
        double y=sc.nextInt();
        double x1=sc.nextInt();
        double y1=sc.nextInt();
        double d;
        d=Math.sqrt((x-x1)*(x-x1)+(y-y1)*(y-y1));
        //System.out.println(d);
        //System.out.println(d/r);
        int ans=(int)(d/r);
        if(d%r==0)
        {
            //System.out.println(d%r);
            if((ans)%2==0)
            {
                System.out.print((ans)/2);
            }
            else
            {
                System.out.print(((ans)/2)+1);
            }
        }
        else
        {
            //System.out.println(d%r);
            System.out.print((ans/2)+1);
        }
        
       
	}
}
