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