#include <bits/stdc++.h>
using namespace std;
signed main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  string s;
  cin >> s;
  int n = (int)s.size();
  map<int, int> mp;
  mp[0] = 0;
  vector<int> dp(n + 1, 1 << 30);
  dp[0] = 0;
  int cur = 0;
  vector<int> candi = {0};
  for (int i = 0; i < 26; i++) candi.push_back(1 << i);
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < 26; j++) {
      if (s[i] - 'a' == j) cur ^= (1 << j);
    }
    for (int x : candi) {
      int y = x ^ cur;
      if (mp.count(y)) dp[i + 1] = min(dp[i + 1], dp[mp[y]] + 1);
    }
    if (!mp.count(cur)) mp[cur] = i + 1;
  }
  cout << dp[n] << endl;
  return 0;
}
