class Map:
 def __init__(self):
 self._entryList = list()

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

 def __contains__(self, key):
 ndx = self._findPosition(key)
 return ndx is not None

 def add(self, key, value):
 ndx = self._findPosition(key)
 if ndx is not None :
 self._entryList[ndx].value = value
 return False
 else :
 entry = _MapEntry(key, value)
 self._entryList.append(entry)
 return True

 def _findPosition(self, key):
 for i in range(len(self)) :
 if self._entryList[i].key == key :
 return i
 return None

 def valueOf(self, key):
 ndx = self._findPosition(key)
 assert ndx is not None, "Invalid map key"
 return self._entryList[ndx].value

 def remove(self, key):
 ndx = self._findPosition(key)
 assert ndx is not None, "Invalid map key"
 self._entryList.pop(ndx)

 def __iter__(self):
 return _MapIterator(self._entryList)

class _MapEntry:
 def __init__(self, key, value):
 self.key = key
 self.value = value

class _MapIterator:
 def __init__(self, entryList):
 self._entryList = entryList
 self.ndx = 0

 def __iter__(self):
 return self

 def __next__(self):
 if self.ndx in range(len(self._entryList)) :
 value = self._entryList[self.ndx].value
 self.ndx += 1
 return value
 else :
 raise StopIteration