#include <bits/stdc++.h>
using namespace std;
using ll = long long;
template <class T>
using V = vector<T>;
template <class T, class U>
using P = pair<T, U>;
using vll = V<ll>;
using vvll = V<vll>;
template <class T>
inline bool chmax(T& a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T>
inline bool chmin(T& a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
const ll MOD = 1000000007;
const ll HIGHINF = (ll)1e18;
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  string s;
  cin >> s;
  ll n = s.size();
  vll a(n + 1, 0);
  for (ll i = 0; i < (ll)n; ++i) a[i + 1] = a[i] ^ (1LL << (s[i] - 'a'));
  vll dp(n + 1, HIGHINF);
  dp[0] = 0;
  vll mdp(1LL << 26, HIGHINF);
  mdp[0] = 0;
  for (ll i = 0; i < (ll)n; ++i) {
    dp[i + 1] = mdp[a[i + 1]] + 1;
    for (ll j = 0; j < (ll)26; ++j) {
      chmin(dp[i + 1], mdp[a[i + 1] ^ (1LL << j)] + 1);
    }
    chmin(mdp[a[i + 1]], dp[i + 1]);
  }
  cout << dp[n] << '\n';
  return 0;
}
