import java.util.Scanner;

public class Fibonacci
{

    public static int fibonacci(int n)
    // precondition:  n >= 1
    // postcondition:  the n^th Fibonacci number has been returned
    {
       if (n == 1 || n == 2) return 1;
       else return
          fibonacci(n-1)  // number of pairs that were around in month n-1
                          //  (they never die)

        + fibonacci(n-2); // number of newborn pairs, which is equal to the
                          // number of pairs that were around in month n-2,
                          // making them old enough to have a pair of babies
                          // of their own in month n
    }

    public static void main(String[] args)
    {
        Scanner Input = new Scanner(System.in);
        System.out.print("Enter number of months: ");
        int n = Input.nextInt();
        System.out.println("\n\nAfter " + n + " months there will be " + 
                           fibonacci(n) + " pairs of rabbits.\n");
    }
}