#include <bits/stdc++.h>
using namespace std;
int p[1 << 26], c[200009], a[26];
string S;
int main() {
  cin >> S;
  for (int i = 0; i < S.size(); i++) {
    a[S[i] - 'a'] ^= 1;
    for (int j = 0; j < 26; j++) c[i + 1] += (a[j] << j);
  }
  for (int i = 0; i < (1 << 26); i++) p[i] = (1 << 30);
  p[0] = 0;
  for (int i = 1; i <= S.size(); i++) {
    for (int j = 0; j < 26; j++) {
      int T = c[i];
      if ((c[i] / (1 << j)) % 2 == 0)
        T += (1 << j);
      else
        T -= (1 << j);
      p[c[i]] = min(p[c[i]], p[T] + 1);
    }
  }
  cout << p[c[S.size()]] << endl;
  return 0;
}
