#include <bits/stdc++.h>
using namespace std;
int iy[] = {0, 0, 1, -1};
int ix[] = {1, -1, 0, 0};
int d[200010], ans;
string s;
int main() {
  cin >> s;
  d[0] = (1 << (s[0] - 'a'));
  for (int i = 1; i < s.size(); i++) {
    d[i] = (d[i - 1] ^ (1 << (s[i] - 'a')));
  }
  int k = 0;
  int j = s.size() - 1;
  while (1 && j >= 0) {
    long long int fl;
    fl = (d[k] | d[j]) - (d[k] & d[j]);
    if ((~((~fl) + (fl & (-fl)))) == 0 || k == j - 1) {
      ans++;
      if (s.size() - 1 == j) {
        cout << ans << endl;
        return 0;
      }
      k = j;
      j = s.size();
    }
    j--;
  }
  cout << ans << endl;
  return 0;
}
