public int numTrees(int n) {

		if (n == 0)
			return 1;
		if (n == 1)
			return 1;

		int sum = 0;

		for (int i = 0; i <= n - 1; i++) {
			sum += numTrees(i) * numTrees(n - 1 - i);
		}

		return sum;

	}