# -*- coding:utf-8 -*-
class Solution:
    def __init__(self):
        self.s1 = []
    def push(self, node):
        self.s1.append(node)
    def pop(self):
        self.s1.pop()
    def top(self):
        return self.s1[-1]
    def min(self):
        return min(self.s1)