#include <bits/stdc++.h>
using namespace std;
const long long linf = 1e18;
const double eps = 1e-12;
const double pi = acos(-1);
template <typename T>
istream& operator>>(istream& is, vector<T>& vec) {
  for (auto&& x : vec) is >> x;
  return is;
}
template <typename T>
ostream& operator<<(ostream& os, const vector<T>& vec) {
  for (long long i = (0), __last_i = (vec.size()); i < __last_i; i++) {
    if (i) os << " ";
    os << vec[i];
  }
  return os;
}
template <typename T>
ostream& operator<<(ostream& os, const vector<vector<T> >& vec) {
  for (long long i = (0), __last_i = (vec.size()); i < __last_i; i++) {
    if (i) os << endl;
    os << vec[i];
  }
  return os;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  string s;
  cin >> s;
  const long long n = s.size();
  vector<long long> v(n + 1, 0);
  vector<long long> cnt(26, 0);
  for (long long i = (0), __last_i = (n); i < __last_i; i++) {
    cnt[s[i] - 'a']++;
    for (long long j = (0), __last_j = (26); j < __last_j; j++) {
      if (cnt[j] % 2 == 1) {
        v[i + 1] |= 1LL << j;
      }
    }
  }
  long long ans = linf;
  vector<long long> dp(1LL << 26, linf);
  dp[0] = 0;
  for (long long i = (0), __last_i = (n); i < __last_i; i++) {
    long long x = v[i + 1];
    long long a = dp[x] + 1;
    for (long long j = (0), __last_j = (26); j < __last_j; j++) {
      a = min(a, dp[x ^ (1LL << j)] + 1);
    }
    dp[v[i + 1]] = min(dp[v[i + 1]], a);
    assert(a < linf);
    if (i == n - 1) ans = a;
  }
  cout << ans << endl;
}
