-- coding:utf-8 --

class Solution: def init(self): self.stack1 = [] self.stack2 = []

def push(self, node):
    # write code here
    self.stack1.append(node)
    
def pop(self):
    # return xx
    if len(self.stack2) != 0:
        return self.stack2.pop()
    else:
        for i in range(len(self.stack1)):
            item = self.stack1.pop()
            self.stack2.append(item)
        return self.stack2.pop()