# Definition for a binary tree node.

# class TreeNode(object):

#     def __init__(self, x):

#         self.val = x

#         self.left = None

#         self.right = None

class Solution(object):

    def minDepth(self, root):

        """

        :type root: TreeNode

        :rtype: int

        """

        if root == None:

            return 0

        if root.left == None and root.right != None:

            return self.minDepth(root.right)+1

        if root.left != None and root.right == None:

            return self.minDepth(root.left)+1

        return min(self.minDepth(root.right),self.minDepth(root.left))+1