import java.util.Scanner;


public class CF_287_B {

    
    public static void main(String[] args) {
        Scanner in = new Scanner (System.in);
        
        double r = in.nextDouble();
        double xOld = in.nextDouble();
        double yOld = in.nextDouble();
        
        double xnew = in.nextDouble();
        double ynew = in.nextDouble();
        
        
        double distane = Math.sqrt(Math.pow(xnew-xOld, 2)+Math.pow(ynew-yOld, 2));
        
        int cycles = (int)(distane/(2*r));
        
        if ( distane%(2*r) != 0)
            cycles++;
                
        System.out.println(cycles);

    }

}
