#include <bits/stdc++.h>
using namespace std;
template <class T1, class T2>
ostream& operator<<(ostream& os, const pair<T1, T2>& a) {
  return os << "(" << a.first << "," << a.second << ")";
}
template <class T>
void pv(T a, T b) {
  for (T i = a; i != b; ++i) cout << (*i) << " ";
  cout << endl;
}
template <class T>
bool chmin(T& a, const T& b) {
  return a > b ? (a = b, 1) : 0;
}
template <class T>
bool chmax(T& a, const T& b) {
  return a < b ? (a = b, 1) : 0;
}
int nextInt() {
  int x;
  scanf("%d", &x);
  return x;
}
int main2() {
  string s;
  cin >> s;
  int N = (int)s.size();
  int b[26] = {0};
  for (int i = 0, _n = (int)(N); i < _n; ++i) ++b[s[i] - 'a'];
  int odd = 0;
  for (int c = 0, _n = (int)(26); c < _n; ++c)
    if (b[c] % 2 == 1) odd++;
  int ans = max(odd, 1);
  cout << ans << endl;
  return 0;
}
int main() {
  for (; !cin.eof(); cin >> ws) main2();
  return 0;
}
