#include <bits/stdc++.h>
using namespace std;
const int inf = 1e9 + 7;
const long long INF = 1LL << 60;
const long long mod = 1e9 + 7;
const long double eps = 1e-8;
const long double pi = acos(-1.0);
template <class T>
inline bool chmax(T& a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T>
inline bool chmin(T& a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
void solve() {
  string s;
  cin >> s;
  long long n = (long long)s.size();
  vector<long long> a(n + 1, 0);
  for (long long i = 0; i < n; i++) {
    a[i + 1] = (a[i] ^ (1 << (s[i] - 'a')));
  }
  vector<long long> x((1 << 26), INF);
  vector<long long> dp(n + 1, INF);
  dp[0] = 0;
  x[0] = 0;
  for (long long i = 0; i < n; i++) {
    for (long long bit = 0; bit < 26; ++bit) {
      long long mask = (1 << bit);
      long long y = a[i + 1] ^ mask;
      chmin(dp[i + 1], x[y] + 1);
      chmin(x[a[i + 1]], dp[i + 1]);
    }
  }
  cout << dp[n] << endl;
}
signed main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  solve();
  return 0;
}
