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