#include <bits/stdc++.h>
using namespace std;
const int INF = 10e+6;
int hash_[200001];
int hash_max[1 << 26];
int dp[200001];
int main() {
  string s;
  cin >> s;
  int N = s.size();
  int cur = 0;
  for (int i = 0; i < (1 << 26); i++) {
    hash_max[i] = 0;
  }
  hash_[0] = 0;
  for (int i = 0; i < N; i++) {
    cur ^= (1 << (s[i] - 'a'));
    hash_[i + 1] = cur;
    dp[i + 1] = INF;
    hash_max[cur] = i + 1;
  }
  dp[0] = 0;
  for (int i = 0; i < N; i++) {
    if (dp[i] >= INF) continue;
    int h = hash_[i];
    if (hash_max[h] > i) dp[hash_max[h]] = min(dp[hash_max[h]], dp[i] + 1);
    for (int j = 0; j < 26; j++) {
      int n = (1 << j);
      h = (hash_[i] ^ n);
      if (hash_max[h] > i) dp[hash_max[h]] = min(dp[hash_max[h]], dp[i] + 1);
    }
  }
  cout << dp[N] << endl;
}
