#include <bits/stdc++.h>
using namespace std;
const int INF = 10e+7;
int hash_[200001];
int hash_max[1 << 26];
int hash_min[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] = -1;
    hash_min[i] = INF;
  }
  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;
  hash_min[0] = 0;
  for (int i = 0; i <= N; i++) {
    int h = hash_[i];
    dp[i] = min(INF, hash_min[h] + 1);
    for (int j = 0; j < 26; j++) {
      int n = (1 << j);
      h = (hash_[i] ^ n);
      dp[i] = min(hash_min[h] + 1, dp[i]);
      hash_min[hash_[i]] = min(hash_min[hash_[i]], dp[i]);
    }
  }
  cout << dp[N] << endl;
}
