#include <bits/stdc++.h>
using namespace std;
ostream &operator<<(ostream &os, const vector<int> &a) {
  os << "[";
  for (int i = 0; i < a.size(); i++) {
    os << a[i];
    if (i < a.size() - 1) os << ",";
  }
  os << "]";
  return os;
}
map<int, int> dp;
int num[252521];
int main() {
  int n, now = 0, out = 0;
  string s;
  cin >> s;
  n = s.size();
  num[0] = 0;
  for (int i = 0; i < n; i++) {
    num[i + 1] = (num[i] ^ (1 << (s[i] - 'a')));
  }
  if (__builtin_popcount(num[n]) < 2) {
    cout << 1 << endl;
    return 0;
  }
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < 26; j++) {
      int t = (num[i] ^ (1 << j));
      if (dp.find(t) == dp.end())
        dp[t] = dp[num[i]] + 1;
      else
        dp[t] = min(dp[t], dp[num[i]] + 1);
    }
  }
  cout << dp[num[n]] << endl;
}
