#include <bits/stdc++.h>
using namespace std;
int main() {
  string S;
  cin >> S;
  map<long long int, vector<long long int>> P;
  P[0] = vector<long long int>(1);
  vector<long long int> Len(S.size(), LONG_MAX / 6);
  Len[0] = 1;
  long long int memo = 0;
  for (int i = 0; i < S.length(); i++) {
    memo ^= (1LL << (S[i] - 'a'));
    if (i == 0) {
      Len[i] = 1;
    } else {
      Len[i] = Len[i - 1] + 1;
      for (auto one : P[memo]) {
        Len[i] = min(Len[one], Len[i]);
      }
    }
    P[memo].push_back(i);
  }
  cout << Len[S.length() - 1] << endl;
}
