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