import re
 
strings = ['A: 45', 'B: 34', 'A: 45, B: 34', 'B: 34, A: 45']
rx = re.compile(r'([AB]): (\d+)')
 
for string in strings:
	groups = [m.groups() for m in rx.finditer(string)]
	sum = 0
	for group in groups:
		(letter, value) = group
		if letter == 'A':
			sum += float(value)
		elif letter == 'B':
			sum -= float(value)
	print(sum)
	#print(groups)
 
"""
Pattern 1: 'A: 45' --> 45 (45 - 0)
 
Pattern 2: 'B: 34' --> -34 (0 - 34)
 
Pattern 3: 'A: 45, B: 34' --> 11 (45 - 34)
 
Pattern 4: 'B: 34, A: 45' --> 11 (45 - 34)# your code goes here
"""

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