#include <bits/stdc++.h>
using namespace std;
const int inf = 1012345678;
int main() {
  cin.tie(0);
  ios_base::sync_with_stdio(false);
  string S;
  cin >> S;
  int N = S.size();
  map<int, int> dp;
  dp[0] = 0;
  int bit = 0;
  for (int i = 0; i < N; ++i) {
    bit ^= 1 << (S[i] - 'a');
    if (dp.find(bit) == dp.end()) {
      int opt = inf;
      for (int j = 0; j < 26; ++j) {
        if (dp.find(bit ^ (1 << j)) != dp.end()) {
          opt = min(opt, dp[bit ^ (1 << j)] + 1);
        }
      }
      dp[bit] = opt;
    }
  }
  cout << (bit == 0 ? 1 : dp[bit]) << '\n';
  return 0;
}
