def main():

    s = eval(input()); total = 0

    for i in range(len(s) // 2):

        if s[i] != s[-i - 1]:

            total += 1

    print(total)

main()
s = eval(input())

n = len(s)//2

count = 0

f = s[:n]   

l = s[-n:]

l = l[::-1]

for i in range(n):

    if f[i] != l[i]:

        count+=1

print(count)
def main():
    s = eval(input())
    total = 0
    for i in range(len(s) // 2):
        if s[i] != s[-i - 1]:
            total += 1
    print(total)


main()

s = eval(input())
n = len(s) // 2
count = 0
f = s[:n]
l = s[-n:]
l = l[::-1]
for i in range(n):
    if f[i] != l[i]:
        count += 1
print(count)

-def main(): -    s = eval(input()) -    total = 0 -    for i in range(len(s) // 2): -        if s[i] != s[-i - 1]: -            total += 1 -    print(total) - - -main() +s = eval(input()) +n = len(s) // 2 +count = 0 +f = s[:n] +l = s[-n:] +l = l[::-1] +for i in range(n): +    if f[i] != l[i]: +        count += 1 +print(count)