#include <bits/stdc++.h>
using namespace std;
const long long inf = 1e9 + 7;
const long long mod = 998244353;
signed main() {
  string s;
  cin >> s;
  long long n = s.size();
  vector<long long> ma(1LL << 26, -1);
  ma[0] = 0;
  long long now = 0;
  long long ans = n;
  for (long long i = (0); i < (n); i++) {
    now ^= (1LL << (s[i] - 'a'));
    long long tmp = inf;
    for (long long j = (0); j < (26); j++) {
      if (ma[(1LL << j) ^ now] != -1) {
        tmp = min(tmp, ma[(1LL << j) ^ now] + 1);
      }
    }
    if (ma[now] != -1) {
      tmp = min(tmp, ma[now]);
    }
    if (tmp != inf) {
      ma[now] = tmp;
      if (i == n - 1) {
        ans = min(ans, tmp);
      }
    }
  }
  if (ans == 0) ans++;
  cout << ans << '\n';
}
