#include <bits/stdc++.h>
using namespace std;
long long cnt[1 << 26];
signed main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout << fixed << setprecision(20);
  string s;
  cin >> s;
  long long n = s.size();
  long long INF = 1e9;
  for (int i = 0; i < (1 << 26); i++) cnt[i] = INF;
  cnt[0] = 0;
  long long now = 0;
  long long ans;
  for (int i = 0; i < n; i++) {
    now ^= (1 << (s[i] - 'a'));
    long long ret = 1e9;
    for (int j = 0; j < 26; j++) {
      ret = min(ret, cnt[now ^ (1 << j)] + 1);
    }
    cnt[now] = min(cnt[now], ret);
    ans = cnt[now];
  }
  ans = max(ans, 1LL);
  cout << ans << endl;
}
