from collections import Counter
s = input()
c = Counter(s)
odd = 0
for x in c:
    if c[x] % 2 == 1:
        odd += 1
print(max(0, odd - 1))

69ef2a86c50c601ce24b7623b8da0ff2306f0184
<mask token>

<mask token>
for x in c:
    if c[x] % 2 == 1:
        odd += 1
print(max(0, odd - 1))

<mask token>
s = input()
c = Counter(s)
odd = 0
for x in c:
    if c[x] % 2 == 1:
        odd += 1
print(max(0, odd - 1))

from collections import Counter
s = input()
c = Counter(s)
odd = 0
for x in c:
    if c[x] % 2 == 1:
        odd += 1
print(max(0, odd - 1))
