#include <bits/stdc++.h>
using namespace std;
int dp[1 << 26];
void solve() {
  string s;
  cin >> s;
  for (int i = 1; i < (1 << 26); i++) dp[i] = 1 << 25;
  int curr = 0;
  for (int i = 0; i < s.size(); i++) {
    curr ^= 1 << (s[i] - 'a');
    for (int x = 0; x < 26; x++) {
      dp[curr] = min(dp[curr], 1 + dp[curr ^ (1 << x)]);
    }
  }
  cout << dp[curr] << "\n";
}
void casesolve() {
  int t;
  cin >> t;
  cin.ignore();
  for (int i = 1; i <= t; i++) {
    cout << "Case #" << i << ": ";
    solve();
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  solve();
}
