#include <bits/stdc++.h>
using namespace std;
const long long INF = (1ll << 60);
int v[1ll << 26];
int main() {
  string s;
  cin >> s;
  for (long long i = 0; i < (1ll << 26); i++) v[i] = INF;
  long long cur = 0ll;
  v[cur] = 0;
  for (char c : s) {
    c -= 'a';
    cur ^= (1ll << c);
    int mi = v[cur];
    for (int i = 0; i < 26; i++) {
      mi = min(mi, v[cur ^ (1ll << i)]);
    }
    v[cur] = mi + 1;
  }
  cout << v[cur] << endl;
}
