s = input()
half = int(len(s) / 2)
left_s = s[:half]
right_s = s[half:]
max_left = 1
max_right = 1
for i in set(left_s):
    max_left = max(max_left,left_s.count(i))
for i in set(right_s):
    max_right = max(max_right,right_s.count(i))
print(len(s) - max_left - max_right)