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