import java.util.Scanner;

public class Solution {
    
    public static void main(String[] args) {
        Scanner cin = new Scanner(System.in);
        int r = cin.nextInt();
        int coord[] = new int[4];
        for (int i = 0; i < coord.length; ++i) {
            coord[i] = cin.nextInt();
        }
        double dist = Math.sqrt(Math.pow((coord[2] - coord[0]), 2) + Math.pow((coord[3] - coord[1]), 2));
        System.out.println((int)Math.ceil(dist / (2 *r)));
        cin.close();
    }
}