class Node:
        content = None
        leftChild = None
        rightChild = None
        def __init__(self, *args):
                self.content = args[0]
                if len(args) >= 3:
                        self.leftChild = args[1]
                        self.rightChild = args[2]

def dfs_inorder(node):
        if node.leftChild:
                print '(',
                dfs_inorder(node.leftChild)
        print node.content,
        if node.rightChild:
                dfs_inorder(node.rightChild)
                print ')',

def dfs_postorder(node):
        if not node:
                return
        dfs_postorder(node.leftChild)
        dfs_postorder(node.rightChild)
        print node.content,

def dfs_preorder(node):
        if not node:
                return
        print node.content,
        dfs_preorder(node.leftChild)
        dfs_preorder(node.rightChild)


def eval(node):
        if node.content == '+':
                return eval(node.leftChild) + eval(node.rightChild)
        elif node.content == '-':
                return eval(node.leftChild) - eval(node.rightChild)
        elif node.content == '*':
                return eval(node.leftChild) * eval(node.rightChild)
        elif node.content == '/':
                return eval(node.leftChild) / eval(node.rightChild)
        else:
                return node.content


root = Node('*', Node('+', Node(3), Node(4)), Node('/', Node(10), Node('-', Node(7), Node(2))))
dfs_inorder(root)
print
dfs_postorder(root)
print
dfs_preorder(root)
print
print eval(root)