#include <bits/stdc++.h>
using namespace std;
bool isP(int val) {
  bool isFound = false;
  for (int i = 0; i < 32; i++) {
    if (val & (1 << i)) {
      if (isFound) {
        return false;
      } else {
        isFound = true;
      }
    }
  }
  return true;
}
int main() {
  string s;
  cin >> s;
  vector<int> state(s.size());
  int bit = 0;
  for (int i = 0; i < s.size(); i++) {
    bit = bit ^ (1 << (s[i] - 'a'));
    state[i] = bit;
  }
  int res = 0;
  for (int i = 0; i < 26; i++) {
    if (state.back() & (1 << i)) {
      res++;
    }
  }
  if (res == 0) res = 1;
  cout << res << endl;
  return 0;
}
