#include <bits/stdc++.h>
using ll = long long;
using P = std::pair<ll, ll>;
constexpr ll INF = 1ll << 60;
template <class T>
inline bool chmax(T& a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T>
inline bool chmin(T& a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class S, class T>
std::ostream& operator<<(std::ostream& out, const std::pair<S, T>& a) {
  std::cout << '(' << a.first << ", " << a.second << ')';
  return out;
}
template <class T>
std::ostream& operator<<(std::ostream& out, const std::vector<T>& a) {
  std::cout << '[';
  for (ll i = (0); i < (a.size()); ++i) {
    std::cout << a[i];
    if (i != a.size() - 1) std::cout << ", ";
  }
  std::cout << ']';
  return out;
}
std::string s;
ll rev(ll bit, ll b) { return bit ^ (1ll << b); }
int main() {
  std::cin >> s;
  ll n = s.size();
  ll par = 0;
  std::vector<ll> dp(n + 10, INF);
  std::vector<ll> memo((1ll << 26) + 10, INF);
  dp[0] = 0;
  memo[0] = 0;
  for (ll i = (0); i < (n); ++i) {
    par = rev(par, s[i] - 'a');
    chmin(dp[i + 1], memo[par] + 1);
    for (ll c = (0); c < (26); ++c) {
      par = rev(par, c);
      chmin(dp[i + 1], memo[par] + 1);
      par = rev(par, c);
    }
    chmin(memo[par], dp[i + 1]);
  }
  std::cout << dp[n] << '\n';
  return 0;
}
