def brackets_error(text):
    pairs = {')': '(', ']': '[', '}': '{'}
    stack = []
    for index, char in enumerate(text):
        if char in '([{':
            stack.append((char, index))
        elif char in pairs:
            if not stack or stack[-1][0] != pairs[char]:
                return index
            stack.pop()
    return stack[-1][1] if stack else None


if __name__ == '__main__':
    print(brackets_error('a[({x})]'))
    print(brackets_error('([)]'))