s = gets.chomp
sum = 0
cusum = [sum]
s.chars{|c|
  cusum << (sum ^= (1 << c.ord - 0x61))
}

$dp = Hash.new 9e9
$dp[0] = 0
(0...cusum.size).each{|i|
  (0..25).each{|n|
    $dp[cusum[i]] = [$dp[cusum[i]], $dp[cusum[i] ^ (1 << n)]+1].min
  }
}
p [1, $dp[cusum[-1]]].max