#include <bits/stdc++.h>
using namespace std;
const int INF =
    sizeof(int) == sizeof(long long) ? 0x3f3f3f3f3f3f3f3fLL : 0x3f3f3f3f;
const int MOD = (int)(1e9) + 7;
const double PI = acos(-1);
const double EPS = 1e-9;
using pii = pair<int, int>;
template <typename T, typename S>
istream &operator>>(istream &is, pair<T, S> &p) {
  is >> p.first >> p.second;
  return is;
}
template <typename T>
void printvv(const vector<vector<T>> &v) {
  cerr << endl;
  for (int i = (0); i < (v.size()); i++)
    for (int j = (0); j < (v[i].size()); j++) {
      if (typeid(v[i][j]) == typeid(INF) and v[i][j] == INF) {
        cerr << "INF";
      } else
        cerr << v[i][j];
      cerr << (j == v[i].size() - 1 ? '\n' : ' ');
    }
  cerr << endl;
}
void YES(bool f) { cout << (f ? "YES" : "NO") << endl; }
void Yes(bool f) { cout << (f ? "Yes" : "No") << endl; }
template <class T>
bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T>
bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
string itob(int x) {
  string ret;
  while (x) {
    if (x & 1)
      ret += "1";
    else
      ret += "0";
    x >>= 1;
  }
  while (ret.size() < 26) ret += "0";
  reverse(begin(ret), end(ret));
  return ret;
}
signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(12);
  string s;
  cin >> s;
  vector<int> dp(1 << 26, INF);
  dp[0] = 1;
  for (int i = (0); i < (26); i++) {
    dp[1 << i] = 1;
  }
  int bits = 0;
  for (int i = (0); i < (s.size()); i++) {
    int a = s[i] - 'a';
    bits ^= 1 << a;
    ;
    for (int j = (0); j < (26); j++) {
      chmin(dp[bits], dp[(1 << j) xor bits] + 1);
    };
  }
  cout << dp[bits] << endl;
  return 0;
}
