public static int findKth(int[] A, int A_start, int[] B, int B_start, int k) {
		if (A_start >= A.length)
			return B[B_start + k - 1];
		if (B_start >= B.length)
			return A[A_start + k - 1];

		if (k == 1)
			return Math.min(A[A_start], B[B_start]);
		
		int A_key = A_start + k / 2 - 1 < A.length ? A[A_start + k / 2 - 1]
				: Integer.MAX_VALUE;

		int B_key = B_start + k / 2 - 1 < B.length ? B[B_start + k / 2 - 1]
				: Integer.MAX_VALUE;

		if (A_key < B_key) {  // we should keep find kth from A_start + k / 2 in A
			return findKth(A, A_start + k / 2, B, B_start, k - k / 2);
		} else { // we should keep find kth from B_start + k / 2 in B
			return findKth(A, A_start, B, B_start + k / 2, k - k / 2);
		}
	}