A = input()
import math
times = math.ceil(len(A) / 2)
count = 0
for i in range(times):
    if A[i] != A[len(A) - 1 - i]:
        count += 1
print(count)

771f034cdf7ec05ee6642f8e0720af2b53da0f2b
<mask token>

<mask token>
for i in range(times):
    if A[i] != A[len(A) - 1 - i]:
        count += 1
print(count)

A = input()
<mask token>
times = math.ceil(len(A) / 2)
count = 0
for i in range(times):
    if A[i] != A[len(A) - 1 - i]:
        count += 1
print(count)

A = input()
import math
times = math.ceil(len(A) / 2)
count = 0
for i in range(times):
    if A[i] != A[len(A) - 1 - i]:
        count += 1
print(count)
