#include <bits/stdc++.h>
using namespace std;
const int INF = 1000000000;
int main() {
  string s;
  cin >> s;
  int n = s.size();
  map<int, int> mp;
  int b = 0;
  for (int i = 0; i < n; i++) {
    b ^= (1 << (s[i] - 'a'));
    if (mp[b]) continue;
    int r = INF;
    for (int j = 0; j < 26; j++) {
      if ((b ^ (1 << j)) == 0) r = 1;
      if (mp[b ^ (1 << j)]) r = min(r, mp[b ^ (1 << j)] + 1);
    }
    mp[b] = r;
  }
  if (b == 0)
    cout << 1 << endl;
  else
    cout << mp[b] << endl;
}
