#include <bits/stdc++.h>
using namespace std;
int cnt[26];
signed main() {
  string s;
  cin >> s;
  for (int i = 0; i < s.size(); i++) cnt[s[i] - 'a']++;
  int ans = 0;
  for (int i = 0; i < 26; i++) {
    if (cnt[i] % 2) ans++;
  }
  if (ans == 1) ans = 0;
  cout << max(1, ans) << endl;
}
