#include <bits/stdc++.h>
using namespace std;
const int INF = 1e9;
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  string S;
  cin >> S;
  int n = S.size();
  vector<int> cnt(n + 1, 0);
  for (int i = 0; i < n; ++i) cnt[i + 1] = cnt[i] ^ (1 << (S[i] - 'a'));
  map<int, int> m;
  for (int i = n; i >= 0; --i) m[cnt[i]] = i;
  vector<int> dp(n + 1, INF);
  dp[0] = 0;
  for (int i = 0; i < n; ++i) {
    if (m.count(cnt[i + 1]) && m[cnt[i + 1]] < i + 1)
      dp[i + 1] = min(dp[i + 1], dp[m[cnt[i + 1]]] + 1);
    for (int j = 0; j < 26; ++j) {
      int mask = cnt[i + 1] ^ (1 << j);
      if (m.count(mask) && m[mask] < i + 1)
        dp[i + 1] = min(dp[i + 1], dp[m[mask]] + 1);
    }
  }
  cout << dp[n] << '\n';
}
