#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  string s;
  cin >> s;
  const int n = s.size();
  vector<int> b(n + 1);
  for (int i = 0; i < n; ++i) {
    const int c = s[i] - 'a';
    b[i + 1] = b[i] ^ (1 << c);
  }
  unordered_map<int, int> mp;
  for (int i = 0; i <= n; ++i) {
    mp[b[i]] = i;
  }
  vector<int> dp(n + 2, n);
  dp[0] = 0;
  for (int i = 0; i < n; ++i) {
    const int te = mp[b[i]];
    dp[te] = min(dp[te], dp[i] + 1);
    for (int c = 0; c < 26; ++c) {
      const int to = mp[b[i] | (1 << c)];
      dp[to] = min(dp[to], dp[i] + 1);
    }
  }
  cout << dp[n] << endl;
  return 0;
}
