/**
 * Program  :   Amr And Pins
 * Platform :   Codeforces
 * URL      :   http://codeforces.com/problemset/problem/507/B
 */

import java.util.Scanner;
public class AmrAndPins{
    public static void main(String args[]){
        Scanner scan = new Scanner(System.in);

        int radius  =   scan.nextInt();
        int x_1     =   scan.nextInt();
        int y_1     =   scan.nextInt();
        int x_2     =   scan.nextInt();
        int y_2     =   scan.nextInt();

        double distance = Math.sqrt(Math.pow((x_2-x_1), 2) + Math.pow((y_2 - y_1),2));

        double res = Math.ceil( distance / 2 * radius );

        System.out.println((int) res);
    }
}