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def subtraction_game(s):
    '''Game loop.'''
    while True:
        s -= user_action(s)
        if (s == 0):
            print('Congratulations! You won!')
            break
        s -= computer_action(s)
        if (s == 0):
            print('You lost! Better luck next time!')
            break


def user_action(s):
    '''User's action selection (by console input).'''
    print('%d matches are on the table. How many do you want to take?' % s)
    amount = 0
    while int(amount) not in CHOICES or int(amount) > s:
        amount = input('> ')
    return int(amount)


def computer_action(s):
    '''Computer's action selection.'''
    amount = nim_strategy(s)
    if not amount:
        from random import choice
        amount = choice(tuple(filter(lambda x: x <= s, CHOICES)))
    print('Computer takes %d matches.' % amount)
    return amount


if __name__ == '__main__':
    subtraction_game(INITSTATE)

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def nim_strategy(s):
.....    

   if s==4:
    return False

   elif s==3:
      return False
   
   elif s==2:
       return False

   elif s==1:
    return False

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def nim_strategy(s):
    choices= 
    
    if s ==choices:
        return False
    
    elif s<=4:
        return False
  

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for i in CHOICES:
		if s > i and not nim_strategy(s-i): return i
	return False