#include <bits/stdc++.h>
using namespace std;
int DP[(1 << 26)] = {};
int main() {
  string str;
  cin >> str;
  for (int i = 0; i < (1 << 26); i++) {
    DP[i] = str.size();
  }
  DP[0] = 0;
  int num = 0;
  for (int i = 0; i < str.size(); i++) {
    num ^= (1 << (str[i] - 'a'));
    int res = DP[num] + 1;
    for (int j = 0; j < 26; j++) {
      int state = (num ^ (1 << j));
      res = min(res, DP[state] + 1);
    }
    DP[num] = min(DP[num], res);
  }
  cout << DP[num] << endl;
  return 0;
}
