#include <bits/stdc++.h>
using namespace std;
long long dp[67108864] = {};
int main() {
  for (int i = 1; i < 67108864; ++i) {
    dp[i] = 2000000000000000000;
  }
  string s;
  cin >> s;
  long long hashing = 0;
  for (int i = 0; i < s.length(); ++i) {
    hashing ^= (1 << (s[i] - 'a'));
    for (int q = 0; q < 26; ++q) {
      long long mew = (1 << q);
      dp[hashing] = min(dp[(mew ^ hashing)] + 1, dp[hashing]);
    }
  }
  cout << dp[hashing] << endl;
  return 0;
}
