#include <bits/stdc++.h>
using namespace std;
bool check(int x) {
  if (x == 0) return true;
  return !(x & (x - 1));
}
int main() {
  string s;
  cin >> s;
  int n = s.size();
  assert(n < 10000);
  vector<int> a(n + 1, 0);
  for (int i = 0; i < n; i++) {
    a[i + 1] = a[i] ^ (1 << (s[i] - 'a'));
  }
  vector<int> opt(n + 1, n + 1);
  opt[0] = 0;
  for (int i = 1; i <= n; i++) {
    for (int j = 0; j < i; j++) {
      if (opt[i] > (opt[j] + 1) && check(a[i] ^ a[j])) opt[i] = opt[j] + 1;
    }
  }
  cout << opt[n] << endl;
  return 0;
}
