#include <bits/stdc++.h>
using namespace std;
const double EPS = 1e-9;
signed main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  string s;
  cin >> s;
  long long n = s.size();
  vector<long long> tmp(n);
  for (long long i = (0); i < (n); i++) tmp[i] = 1LL << (s[i] - 'a');
  for (long long i = (0); i < (n - 1); i++) tmp[i + 1] ^= tmp[i];
  vector<long long> dp(n + 1, (1LL << 60)), dp2(1LL << 26, (1LL << 60));
  dp[0] = 0, dp2[0] = 0;
  for (long long i = (0); i < (n); i++) {
    long long mn = dp2[tmp[i]] + 1;
    for (long long j = (0); j < (26); j++)
      mn = min(mn, dp2[tmp[i] ^ (1LL << j)] + 1);
    dp[i + 1] = mn;
    dp2[tmp[i]] = min(mn, dp2[tmp[i]]);
  }
  cout << dp[n] << endl;
  return 0;
}
