import java.util.Scanner;

/**
 * Created by yuu on 26/3/17.
 */
public class Problem507B {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int r = sc.nextInt();
        int x1 = sc.nextInt();
        int y1 = sc.nextInt();
        int x2 = sc.nextInt();
        int y2 = sc.nextInt();
        double distance = Math.sqrt(Math.pow(x1-x2, 2) + Math.pow(y1-y2, 2));
        int result = (int)Math.ceil(distance/2/r);
        System.out.println(result);
    }
}
