#include <bits/stdc++.h>
using namespace std;
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  vector<int> cnt(26);
  string s;
  cin >> s;
  for (auto t : s) {
    cnt[t - 'a']++;
  }
  int ans = 0;
  for (auto t : cnt) {
    ans += (t & 1);
  }
  ans = max(ans, 1);
  cout << ans << endl;
}
