class Stack:
    def __init__(self):
        self.values = []
        self.key_values = {}
        self.pop = self.values.pop

    def __len__(self):
        return len(self.values)

    def __str__(self):
        return str(self.values)

    def push(self,value):
        self.values.append(value)
        if type(value[0]) != list:
            self.key_values[value[0]] = value[1:]

    def peek(self,index=False):
        if len(self.values) > 0:
            if not index:
                return self.values[-1]
            else:
                return self.values[index]
        return [None,None]

    def get_values(self,reverse=False):
        out = []
        if not reverse:
            for item in self.values:
                out += item[0]
        else:
            for i in range(len(self.values)-1,-1,-1):
                out += self.values[i][0]
        return out