#include <bits/stdc++.h>
const int INF = 1e9;
using namespace std;
template <typename T, typename U>
ostream& operator<<(ostream& os, const pair<T, U>& p) {
  cout << '(' << p.first << ' ' << p.second << ')';
  return os;
}
template <typename T>
void dpite(T a, T b) {
  return;
}
template <typename T>
void pite(T a, T b) {
  for (T ite = a; ite != b; ite++) cout << (ite == a ? "" : " ") << *ite;
  cout << '\n';
}
template <typename T>
bool chmax(T& a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T>
bool chmin(T& a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
void ios_init() {
  ios::sync_with_stdio(false);
  cin.tie(0);
}
int main() {
  ios_init();
  string s;
  while (cin >> s) {
    map<char, int> cnt;
    for (int i = (0); i < (int((s).size())); ++i) {
      cnt[s[i]]++;
    }
    dpite((cnt).begin(), (cnt).end());
    int ans = 0;
    for (auto&& e : cnt) {
      if (e.second % 2 == 1) {
        ans++;
      }
    }
    if (ans != 0)
      cout << ans << '\n';
    else
      cout << 1 << '\n';
  }
  return 0;
}
