#include <bits/stdc++.h>
using namespace std;
string s;
map<int, int> mp, cnt;
int main() {
  cin >> s;
  int cur = 0, x;
  cnt[0] = 1;
  for (int i = 0; i < s.size(); ++i) {
    cur ^= (1 << (s[i] - 'a'));
    if (cur == 0) {
      continue;
    } else {
      if (cnt[cur] == 0) cnt[cur] = 1e8;
      for (int j = 0; j < 26; ++j) {
        if ((cur ^ (1 << j)) == 0) {
          cnt[cur] = 1;
          break;
        } else {
          if (cnt[cur ^ (1 << j)] > 0)
            cnt[cur] = min(cnt[cur], cnt[cur ^ (1 << j)] + 1);
          else {
            cnt[cur] = min(cnt[cur], cnt[cur ^ (1 << (s[i] - 'a'))] + 1);
          }
        }
      }
    }
  }
  cout << cnt[cur] << endl;
}
