#include <bits/stdc++.h>
using namespace std;
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  string s;
  cin >> s;
  unordered_map<long long int, long long int> m;
  m[0] = 0;
  long long int xr = 0;
  for (long long int i = 0; i < (long long int)(s.length()); i++) {
    xr ^= (1 << (s[i] - 'a'));
    long long int ans = 1e9;
    for (long long int bi = 0; bi < 26; bi++) {
      if (xr & (1 << bi) && m.find((xr ^ (1 << bi))) != m.end()) {
        ans = min(ans, m[(xr ^ (1 << bi))] + 1);
      }
    }
    if (ans <= s.length()) {
      if (m.find(xr) != m.end())
        m[xr] = ans;
      else
        m[xr] = ans;
    }
  }
  if (xr == 0)
    cout << 1;
  else
    cout << m[xr];
}
