#include <bits/stdc++.h>
using namespace std;
const int INF = 1e9 + 239;
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  vector<int> cnt(26);
  string s;
  cin >> s;
  int cm = 0;
  map<int, int> dpmin;
  dpmin[cm] = 0;
  for (auto t : s) {
    cm ^= (1 << (t - 'a'));
    int cdp = INF;
    if (dpmin.count(cm)) cdp = dpmin[cm];
    for (int j = 0; j < 26; j++) {
      if (dpmin.count(cm ^ (1 << j))) cdp = min(cdp, dpmin[cm ^ (1 << j)]);
    }
    cdp++;
    if (!dpmin.count(cm)) dpmin[cm] = INF;
    dpmin[cm] = min(dpmin[cm], cdp);
  }
  cout << dpmin[cm] << endl;
}
