#include <bits/stdc++.h>
using namespace std;
int main() {
  string S;
  cin >> S;
  int N = S.size();
  vector<int> X(N + 1, 0);
  for (int i = 1; i <= N; i++) {
    X[i] = X[i - 1] ^ (1 << ((S[i - 1] - 'a')));
  }
  map<int, int> memo;
  vector<int> dp(N + 1, 1e9);
  memo[0] = 0;
  dp[0] = 0;
  for (int i = 1; i <= N; i++) {
    int val = X[i];
    if (memo.count(val)) {
      dp[i] = memo[val] + 1;
    }
    for (int j = 0; j < 26; j++) {
      int key = (1 << j);
      int pre = val ^ key;
      if (memo.count(pre)) {
        dp[i] = min(dp[i], memo[pre] + 1);
      }
    }
    if (!memo.count(val)) memo[val] = dp[i];
  }
  cout << dp[N] << endl;
}
