#include <bits/stdc++.h>
using namespace std;
constexpr long long INF = 1e18;
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;
}
signed main() {
  string s;
  cin >> s;
  vector<int> next(1 << 26, 333333);
  next[0] = 0;
  int now = 0;
  for (int i = (0); i < (int)(s.size()); i++) {
    now ^= 1 << (s[i] - 'a');
    next[now] = i;
  }
  now = 0;
  vector<int> dp(s.size() + 1, s.size() + 1);
  dp[0] = 0;
  for (int i = (0); i < (int)(s.size()); i++) {
    CHMIN(dp[i + 1], dp[i] + 1);
    for (int j = (0); j < (int)(26); j++)
      if (next[now ^ (1ll << j)] != 333333)
        CHMIN(dp[next[now ^ (1ll << j)] + 1], dp[i] + 1);
    now ^= 1 << (s[i] - 'a');
  }
  if (now)
    cout << dp[s.size()] << endl;
  else
    cout << 1 << endl;
}
