Algorithm - hw#1

import java.util.Scanner;
class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int num = scanner.nextInt();
        System.out.println(f(num));
    }
    public static int f(int n) {
        if (n == 1)
            return 1;
        else {
            int sum = 0;
            for(int k = 1;k < n;k++)
              sum = sum + f(k) * f(n - k);
            return sum;
        }
    }
}