#include <bits/stdc++.h>
using namespace std;
int num[(1 << 26)];
int cur = 0;
signed main() {
  memset(num, -1, sizeof(num));
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  string s;
  cin >> s;
  num[0] = 0;
  for (int i = 0; i < s.size(); i++) {
    cur ^= 1 << (s[i] - 'a');
    for (int i = 0; i < 26; i++) {
      int mask = cur ^ (1 << i);
      if (num[mask] == -1) continue;
      if (num[cur] == -1) num[cur] = num[mask] + 1;
    }
  }
  if (cur == 0)
    cout << 1;
  else
    cout << num[cur];
}
