#include <bits/stdc++.h>
using namespace std;
int alp[26], res;
string s;
int main() {
  cin >> s;
  for (int i = 0; i < s.size(); ++i) {
    alp[s[i] - 'a']++;
  }
  for (int i = 0; i < 26; ++i) {
    res += alp[i] & 1;
  }
  cout << max(res, 1) << endl;
}
