#include <bits/stdc++.h>
using namespace std;
void Debug() { cout << '\n'; }
template <class FIRST, class... REST>
void Debug(FIRST arg, REST... rest) {
  cout << arg << " ";
  Debug(rest...);
}
template <class T>
ostream& operator<<(ostream& out, const vector<T>& v) {
  out << "[";
  if (!v.empty()) {
    for (int i = int(0); i < int((int)(v).size() - 1); i++) out << v[i] << ", ";
    out << v.back();
  }
  out << "]";
  return out;
}
template <class S, class T>
ostream& operator<<(ostream& out, const pair<S, T>& v) {
  out << "(" << v.first << ", " << v.second << ")";
  return out;
}
const int MAX_N = 200010;
const int MAX_V = 100010;
const double eps = 1e-6;
const long long mod = 1000000007;
const int inf = 1 << 29;
const long long linf = 1LL << 60;
const double PI = 3.14159265358979323846;
int N;
string str;
int B[MAX_N];
int dp[(1 << 26)];
void solve() {
  cin >> str;
  N = (int)(str).size();
  for (int i = int(0); i < int(N); i++) {
    int s = str[i] - 'a';
    B[i + 1] = (1 << s) ^ B[i];
  }
  for (int i = int(0); i < int((1 << 26)); i++) dp[i] = inf;
  dp[0] = 0;
  for (int i = int(0); i < int(N); i++) {
    for (int j = int(0); j < int(26); j++) {
      int to = B[i + 1] ^ (1 << j);
      dp[B[i + 1]] = min(dp[B[i + 1]], dp[to] + 1);
    }
  }
  cout << dp[B[N]] << "\n";
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout << fixed;
  cout.precision(20);
  srand((unsigned int)time(NULL));
  solve();
  return 0;
}
