class Solution(object):
    def inorderSuccessor(self, q):
        """
        :type q: TreeNode
        :rtype: TreeNode
        """
        if q.right:
            q = q.right
            while (q.left):
                q = q.left
            return q

        while q.father and q.father.right == q:
            q = q.father
        return q.father