#include <bits/stdc++.h>
using namespace std;
const long long int MOD = 1000000007;
long long int N, M, K, H, W, L, R;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  string s;
  cin >> s;
  vector<int> dp(1 << 26, MOD);
  dp[0] = 0;
  int cbit = 0;
  int ans = MOD;
  for (auto i : s) {
    ans = MOD;
    int box = i - 'a';
    cbit ^= 1 << box;
    for (int j = 0; j < 26; j++) {
      ans = min(ans, dp[cbit ^ 1 << j] + 1);
    }
    ans = min(ans, dp[cbit] + 1);
    dp[cbit] = min(cbit, ans);
  }
  cout << ans << endl;
  return 0;
}
