#include <bits/stdc++.h>
using namespace std;
long long dp[1 << 26];
long long val[214514];
long long ans[214514];
signed main() {
  string str;
  cin >> str;
  long long n = str.size();
  for (long long i = 1; i <= n; i++) {
    long long cur = str[i - 1] - 'a';
    val[i] = val[i - 1] ^ (1 << cur);
  }
  for (long long i = 0; i < (1 << 26); i++) {
    dp[i] = 1000000007;
  }
  dp[0] = 0;
  for (long long i = 1; i <= n; i++) {
    vector<long long> v;
    long long cur = val[i];
    v.push_back(dp[cur]);
    for (long long j = 0; j < 26; j++) {
      v.push_back(dp[cur ^ (1 << j)]);
    }
    sort(v.begin(), v.end());
    ans[i] = v[0] + 1;
    dp[cur] = min(dp[cur], ans[i]);
  }
  cout << ans[n] << endl;
  return 0;
}
