#include <bits/stdc++.h>
using namespace std;
template <typename T>
using V = vector<T>;
int N;
string S;
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cin >> S;
  N = S.size();
  V<int> DP(1 << 26, 1e9);
  DP[0] = 0;
  int bs = 0, res;
  for (int(i) = 0; (i) < (N); ++(i)) {
    bs ^= (1 << (S[i] - 'a'));
    int ans = 1e9;
    for (int(c) = 0; (c) < (26); ++(c)) ans = min(ans, DP[bs ^ (1 << c)]);
    DP[bs] = min(DP[bs], ans + 1);
    res = ans + 1;
  }
  cout << res << endl;
}
