#include <bits/stdc++.h>
using namespace std;
int cnt[100], cnt2[100];
string s;
int main() {
  cin >> s;
  int n = s.size();
  for (long long i = (long long)(0); i < (long long)(n); i++) {
    cnt[s[i] - 'a']++;
  }
  int tmp = 0;
  int res = 0;
  for (long long i = (long long)(0); i < (long long)(26); i++) {
    if (cnt[i] % 2 == 1) tmp++;
  }
  if (tmp == 0)
    cout << 1 << endl;
  else {
    vector<int> k;
    int st = 0;
    for (long long i = (long long)(0); i < (long long)(n); i++) {
      cnt2[s[i] - 'a']++;
      if (cnt2[s[i] - 'a'] % 2 == 1) {
        k.push_back(s[i] - 'a');
      } else {
        int tmp2;
        for (long long j = (long long)(0); j < (long long)(k.size()); j++) {
          if (k[j] == s[i] - 'a') {
            tmp2 = j;
            break;
          }
        }
        k.erase(k.begin() + tmp2);
      }
      if (k.size() == 1 && cnt[s[i] - 'a'] % 2 == 1) {
        cnt[s[i] - 'a'] = 0;
        res++;
        st = i + 1;
        k.clear();
        memset(cnt2, 0, sizeof(cnt2));
      }
      if (k.size() == 2 && cnt[k[0]] % 2 == 1 && cnt[k[1]] % 2 == 1) {
        res++;
        i = st;
        k.clear();
      }
    }
    cout << res << endl;
  }
  return 0;
}
