s = list(input())
cnt = 0
while len(s) > 1:
    if s.pop(0) == s.pop(-1):
        pass
    else:
        cnt += 1
print(cnt)

3b8ddb840c09bc031ffadc3f5e659bc54f9eafd0
<mask token>

<mask token>
while len(s) > 1:
    if s.pop(0) == s.pop(-1):
        pass
    else:
        cnt += 1
print(cnt)

s = list(input())
cnt = 0
while len(s) > 1:
    if s.pop(0) == s.pop(-1):
        pass
    else:
        cnt += 1
print(cnt)
