#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int INF = 1e9;
int main() {
  string s;
  cin >> s;
  int n = s.length();
  map<int, int> mp;
  vector<int> a(n + 1);
  int v = 0;
  for (int i = 0; i < (int)n; i++) {
    int c = s[i] - 'a';
    v ^= (1 << c);
    a[i + 1] = v;
    mp[v] = i + 1;
  }
  if (v == 0) {
    cout << 1 << endl;
    return 0;
  }
  vector<int> dp(n + 1, INF);
  dp[0] = 0;
  for (int i = 0; i < (int)n; i++) {
    for (int j = 0; j < (int)26; j++) {
      int b = (a[i] ^ (1 << j));
      if (mp[b] > i) dp[mp[b]] = min(dp[mp[b]], dp[i] + 1);
    }
  }
  cout << dp[n] << endl;
  return 0;
}
