public int find_index(int[] A, int left, int right, int target) {
		if (left > right)
			return -1;
		int mid = left + (right - left) / 2;
		if (A[mid] == target)
			return mid;
		if (A[mid] > target)
			return find_index(A, left, mid - 1, target);
		else {
			return find_index(A, mid + 1, right, target);
		}
	}