#include <bits/stdc++.h>
using namespace std;
int main() {
  string s;
  cin >> s;
  int N = (int)s.size();
  vector<int> T(1 << 26, N);
  T[0] = 0;
  int h = 0;
  for (int i = 0; i < (int)s.size(); i++) {
    h ^= 1 << (s[i] - 'a');
    int a = N;
    for (int i = 0; i < 26; i++) a = min(a, T[h ^ 1 << i] + 1);
    T[h] = min(T[h], a);
  }
  cout << T[h] << endl;
}
