#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using vi = vector<int>;
using vl = vector<ll>;
using vvi = vector<vi>;
using vvl = vector<vl>;
const ll INF = 1LL << 60;
const ll MOD = 1000000007;
template <class T>
bool chmax(T &a, const T &b) {
  return (a < b) ? (a = b, 1) : 0;
}
template <class T>
bool chmin(T &a, const T &b) {
  return (b < a) ? (a = b, 1) : 0;
}
template <class C>
void print(const C &c, std::ostream &os = std::cout) {
  std::copy(std::begin(c), std::end(c),
            std::ostream_iterator<typename C::value_type>(os, " "));
  os << std::endl;
}
int main() {
  string s;
  cin >> s;
  int n = s.size();
  vector<int> cnt(1 << 26, 1 << 29);
  cnt[0] = 0;
  ll curr = 0;
  for (int i = 0; i < n; ++i) {
    int t = 1 << 29;
    curr ^= 1 << (s[i] - 'a');
    for (int j = 0; j < 27; ++j) {
      ll temp = curr ^ (1 << j);
      if (j == 26) temp = curr;
      chmin(t, 1 + cnt[temp]);
    }
    chmin(cnt[curr], t);
  }
  cout << cnt[curr] << "\n";
  return 0;
}
