#include <bits/stdc++.h>
using namespace std;
using Int = long long;
signed main() {
  string s;
  cin >> s;
  int n = s.size();
  vector<int> v(n + 1);
  v[0] = 0;
  for (int i = 0; i < n; i++) {
    v[i + 1] = v[i] ^ (1 << (s[i] - 'a'));
  }
  vector<int> dp(n + 1, 1 << 28);
  map<int, int> mm;
  dp[0] = 0;
  for (int i = 0; i <= n; i++) {
    int b = v[i];
    if (!mm.count(b)) mm[b] = dp[i];
    for (int j = 0; j < 26; j++) {
      b ^= (1 << j);
      if (mm.count(b)) dp[i] = min(dp[i], mm[b] + 1);
      b ^= (1 << j);
    }
    dp[i + 1] = min(dp[i + 1], dp[i] + 1);
  }
  cout << dp[n] << endl;
  return 0;
}
