#include <bits/stdc++.h>
using namespace std;

int main() {

  ios::sync_with_stdio(false);
  cout.tie(nullptr);
  cin.tie(nullptr);

  string s;
  cin >> s;

  vector<int> dp(1<<26, 1e7);
  dp[0] = 0;
  int hash = 0, n = (int)s.size();

  for (int i = 0; i < n; ++i) {
    hash ^= (1<<(s[i] - 'a'));
    for (int j = 0; j < 26; ++j) {
      dp[hash] = min(dp[hash], 1 + dp[hash ^ (1<<j)]);
    }
  }

  cout << max(1, dp[hash]) << '\n';
}




