#include <bits/stdc++.h>
using namespace std;
long long dp[1 << 27] = {0};
int main() {
  string s;
  cin >> s;
  vector<long long> hs;
  long long now_h = 0;
  long long n = s.length();
  for (int i = 0; i < n; i++) {
    long long c = (long long)(s[i] - 'a');
    now_h ^= ((long long)1 << c);
    hs.push_back(now_h);
  }
  for (int i = 0; i < (1 << 27); i++) dp[i] = 174417441744;
  dp[0] = 0;
  for (int i = 0; i < n; i++) {
    dp[hs[i]]++;
    for (int j = 0; j < 26; j++) {
      if (hs[i] == (1 << j)) dp[hs[i]] = 1;
      dp[hs[i]] = min(dp[hs[i]], dp[hs[i] ^ (1 << j)] + 1);
    }
  }
  cout << dp[hs[n - 1]] << endl;
}
