import java.util.Scanner;
import java.util.InputMismatchException;

public class Fibonacci
{
   // prints the n-th fibonacciNumber

   public static int fibonacciNumber(int n) {
      if ( n < 1 ) {
         return 0;
      } else if ( n == 1 ) {
         return 1;
      } else {
         return fibonacciNumber(n-1) + fibonacciNumber(n-2);
      }
   }

   public static int iterativeFibonacciNumber(int n) {
      if ( n < 1 ) {
         return 0;
      } else if ( n == 1 ) {
         return 1;
      }

      int arr[] = new int[n+1];

      arr[0] = 0;
      arr[1] = 1;

      for ( int i = 2; i < n+1; i++ ) {
         arr[i] = arr[i-1] + arr[i-2];
      }

      return arr[arr.length - 1];
   }

   public static void main (String[] args) {
      int n = 0;

      if ( args.length > 0 ) {
         try {
            n = Integer.parseInt(args[0]); 
         } catch ( NumberFormatException  nfe ) {
            // System.err.println("Invalid input.");
         }
      }

      if ( n == 0 ) { // either no input is given through command line, or the input was invalid.
         System.out.print("Enter a number, n >= 1, and I will print the n-th Fibonacci number: ");

         try {
            Scanner keyboard = new Scanner(System.in);
            n = keyboard.nextInt();
         } catch ( InputMismatchException ime ) {
            System.err.println("Invalid input.");
            System.exit(1);
         }

         if ( n < 1 ) {
            System.err.println("Number must be greater than 0.");
            System.exit(1);
         }
      }

      if ( (args.length == 1 && args[0].compareTo("-i") == 0) ||
           (args.length == 2 && args[1].compareTo("-i") == 0) ) { // iterative version is asked
         System.out.printf("The %d-th Fibonacci number is: %d.\n", n, iterativeFibonacciNumber(n));
      } else {
         System.out.printf("The %d-th Fibonacci number is: %d.\n", n, fibonacciNumber(n));
      }
   }
}