#include <bits/stdc++.h>
using namespace std;
void Solve() {
  string s;
  cin >> s;
  vector<int> v(30);
  for (int i = 0; i < s.length(); ++i) {
    v[s[i] - 'a']++;
  }
  int ans = 0;
  for (int i = 0; i < 26; ++i) {
    if (v[i] & 1) {
      ++ans;
    }
  }
  if (ans == 0) ans = 1;
  cout << ans << "\n";
}
int main() {
  int tests = 1;
  for (; tests; --tests) {
    Solve();
  }
}
