#include <bits/stdc++.h>
using namespace std;
bool palindrome(string s) {
  string t = s;
  reverse(t.begin(), t.end());
  return t == s;
}
string s;
int a[128];
int main() {
  cin >> s;
  for (auto x : s) {
    a[x]++;
  }
  int cnt = 0;
  for (int i = 'a'; i <= 'z'; ++i) {
    cnt += (a[i] & 1);
  }
  cout << max(1, cnt) << endl;
  return 0;
}
