#include <bits/stdc++.h>
using namespace std;
int mask[222222];
long long dp[222222];
int main() {
  string S;
  cin >> S;
  mask[0] = 0;
  for (int i = 0; i < S.size(); i++) {
    mask[i + 1] = mask[i];
    mask[i + 1] ^= (1 << (S[i] - 'a'));
  }
  map<int, int> mask_to_ids;
  mask_to_ids[0] = 0;
  int L = S.size();
  for (int i = 1; i <= L; i++) {
    dp[i] = 1000000000;
    if (mask_to_ids.find(mask[i]) != mask_to_ids.end()) {
      dp[i] = min(dp[i], 1 + dp[mask_to_ids[mask[i]]]);
    }
    for (int c = 0; c < 26; c++) {
      int rmask = (mask[i] ^ (1 << c));
      if (mask_to_ids.find(rmask) != mask_to_ids.end()) {
        dp[i] = min(dp[i], 1 + dp[mask_to_ids[rmask]]);
      }
    }
    if (mask_to_ids.find(mask[i]) == mask_to_ids.end()) {
      mask_to_ids[mask[i]] = i;
    }
  }
  cout << dp[L] << endl;
}
