#include <bits/stdc++.h>
using namespace std;
int main() {
  string S;
  cin >> S;
  int a = 'z' - 'a' + 1;
  int n = S.size();
  vector<int> hash(n + 1);
  for (int i = 0; i < (int)(n); i++) {
    int b = 1 << (S[i] - 'a');
    hash[i + 1] = hash[i] ^ b;
  }
  vector<int> dp(1 << a, n);
  dp[0] = 1;
  for (int i = 0; i < (int)(a); i++) dp[1 << i] = 1;
  for (int i = 0; i < (int)(n); i++) {
    int h = hash[i + 1];
    for (int j = 0; j < (int)(a); j++) {
      int b = hash[i + 1] ^ (1 << j);
      dp[h] = min(dp[h], dp[b] + 1);
    }
  }
  cout << dp[hash[n]] << endl;
  return 0;
}
