#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, 0), dp(n + 1, n + 1), m(1 << 26, n + 1);
  for (int i = 0; i < n; i++) v[i + 1] = v[i] ^ (1 << (s[i] - 'a'));
  for (int i = 0; i <= n; i++) {
    int b = v[i];
    m[b] = min(m[b], dp[i]);
    dp[i] = min(dp[i], m[b] + 1);
    for (int j = 0; j < 26; j++) dp[i] = min(dp[i], m[b ^ (1 << j)] + 1);
    m[b] = min(m[b], dp[i]);
  }
  cout << dp[n] << endl;
  return 0;
}
