import java.util.Scanner;


public class B287 {

    public static void main(String[] args) {
        
        Scanner sc=new Scanner(System.in);
        
        double r=sc.nextDouble();
        
        double x1=sc.nextDouble();
        double y1=sc.nextDouble();
        
        double x2=sc.nextDouble();
        double y2=sc.nextDouble();
        
        
        double x=x2-x1;
        x*=x;
        
        double y=y2-y1;
        y*=y;
        
        int c=0;
        double p=Math.sqrt(x+y);
        
        if(p>=r){
            p-=r;
            c++;
        }
        while(p>=r*2){
            p-=r*2;
            c++;
        }

        if(p>r)
            c++;
        
        System.out.println(c);
    }
}
