#include <bits/stdc++.h>
using namespace std;
int main() {
  string s;
  cin >> s;
  int n = s.size();
  vector<int> alphabit(n + 1);
  for (int i = 0; i < n; i++) {
    alphabit[i + 1] = alphabit[i] ^ (1 << (s[i] - 'a'));
  }
  vector<int> dp(n + 1, n);
  dp[0] = 0;
  map<int, int> mp;
  mp[0] = 0;
  for (int i = 0; i < n; i++) {
    for (int j = 0; j <= 'z' - 'a'; j++) {
      int v = alphabit[i + 1] ^ (1 << j);
      if (mp.count(v)) {
        dp[i + 1] = min(dp[i + 1], dp[mp[v]] + 1);
      }
    }
    if (mp.count(alphabit[i + 1])) {
      dp[i + 1] = min(dp[i + 1], dp[mp[alphabit[i + 1]]] + 1);
    }
    if (!mp.count(alphabit[i + 1])) mp[alphabit[i + 1]] = i + 1;
  }
  cout << dp[n] << endl;
  return 0;
}
