new_contents: class MinStack:
  
      def __init__(self):
          self.stk = []
          self.min = []
  
      # @param x, an integer
      # @return an integer
      def push(self, x):
          self.stk.append(x)
          if not self.min or self.min[-1] >= x:
              self.min.append(x)
  
      # @return nothing
      def pop(self):
          if self.stk[-1] == self.min[-1]:
              self.min.pop()
          self.stk.pop()
  
      # @return an integer
      def top(self):
          return self.stk[-1]
  
      # @return an integer
      def getMin(self):
          return self.min[-1]
  
subject: add Solution for Min Stack