def special_format(n):
	s, *d = str(n).partition(".")
	r = ",".join([s[x-2:x] for x in range(-3, -len(s), -2)][::-1] + [s[-3:]])
	return "".join([r] + d)
 
print(special_format(1))
print(special_format(12))
print(special_format(123))
print(special_format(1234))
print(special_format(12345))
print(special_format(123456))
print(special_format(12345678901234567890))
print(special_format(1.0))
print(special_format(12.34))
print(special_format(1234567890.1234567890))
 

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