#include <bits/stdc++.h>
using namespace std;
int main(void) {
  string s;
  cin >> s;
  int m[256];
  for (int i = (0); i < (26); ++i) m['a' + i] = (1 << i);
  int tmp = 0;
  map<int, int> d;
  d[0] = 0;
  for (auto i = s.begin(); i != s.end(); ++i) {
    tmp = (tmp ^ m[*i]);
    d[tmp] = 33554432;
    for (int j = (0); j < (26); ++j)
      if (d.count(tmp ^ (1 << j))) d[tmp] = min(d[tmp], d[tmp ^ (1 << j)] + 1);
  }
  cout << max(1, d[tmp]) << endl;
  return 0;
}
