#include <bits/stdc++.h>
using namespace std;
int main() {
  string s;
  cin >> s;
  vector<int> cnt(26);
  for (auto c : s) cnt[c - 'a']++;
  int od = 0;
  for (int i = 0; i < 26; ++i) od += cnt[i] % 2;
  cout << max(1, od) << endl;
}
