#include <bits/stdc++.h>
const int MOD = 1e9 + 7;
const int iINF = 2147483647 / 2;
const long long int llINF = 9223372036854775807 / 2;
using namespace std;
using ll = long long int;
using vl = vector<ll>;
using vvl = vector<vector<ll>>;
using vvvl = vector<vector<vector<ll>>>;
bool paircomp(const pair<ll, ll> &a, const pair<ll, ll> &b) {
  if (a.first == b.first) return a.second < b.second;
  return a.first < b.first;
}
ll POW(ll n, ll m) {
  if (m == 0) {
    return 1;
  } else if (m % 2 == 0) {
    ll tmp = POW(n, m / 2);
    return (tmp * tmp);
  } else {
    return (n * POW(n, m - 1));
  }
}
int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  string S;
  cin >> S;
  ll N = S.size();
  vl DP(N + 1);
  vl L(1LL << 26, -1);
  for (ll i = 0; i < (N); i++) {
    DP[i + 1] = DP[i] ^ (1LL << (S[i] - 'a'));
    L[DP[i + 1]] = i + 1;
  }
  vl DDP(N + 1, llINF);
  vl DDPC(N + 1, llINF);
  DDP[0] = 0;
  DDPC[0] = 0;
  for (ll i = 0; i < (N); i++) {
    ll po = DP[i];
    DDP[L[po]] = min(DDPC[L[po]], DDPC[i] + 1);
    for (ll j = 0; j < (26); j++) {
      ll yo = po ^ (1 << j);
      if (L[yo] > i) DDP[L[yo]] = min(DDPC[L[yo]], DDPC[i] + 1);
    }
    DDPC = DDP;
  }
  cout << DDP[N] << endl;
  return 0;
}
