#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using PII = pair<ll, ll>;
template <typename T>
void chmin(T &a, const T &b) {
  a = min(a, b);
}
template <typename T>
void chmax(T &a, const T &b) {
  a = max(a, b);
}
struct FastIO {
  FastIO() {
    cin.tie(0);
    ios::sync_with_stdio(0);
  }
} fastiofastio;
const ll INF = 1LL << 60;
int main(void) {
  string s;
  cin >> s;
  const ll n = s.size();
  ll rui = 0;
  vector<ll> dp1(n), dp2(1LL << 26, INF);
  dp1[0] = dp2[0] = 0;
  for (ll i = (ll)0; i < (ll)n; ++i) {
    rui ^= 1LL << (s[i] - 'a');
    ll mi = dp2[rui];
    for (ll j = (ll)0; j < (ll)26; ++j) chmin(mi, dp2[rui ^ (1LL << j)]);
    dp1[i] = mi + 1;
    chmin(dp2[rui], dp1[i]);
  }
  cout << dp1[n - 1] << endl;
  return 0;
}
