import java.util.*;

public class MyClass {
    
    public static void main(String args[]) {
      Scanner s = new Scanner(System.in);
      int n = s.nextInt();
      int a  = s.nextInt();
      int b = s.nextInt();
      int c = s.nextInt();
      int d = s.nextInt();
      double ans  = ar(a,b,c,d);
    //  System.out.println(ans/2*n);
      ans = Math.ceil(ans/(2*n));
      System.out.println((int)ans);
    }
    public static double ar(
      int x1, 
      int y1, 
      int x2, 
      int y2) {       
        return Math.sqrt((y2 - y1) * (y2 - y1) + (x2 - x1) * (x2 - x1));
    }
}