#include <bits/stdc++.h>
using namespace std;
const long long int E = 1e18 + 7;
const long long int MOD = 1000000007;
vector<int> A(1LL << 26, -1);
int main() {
  string s;
  cin >> s;
  long long int n = s.size();
  vector<long long int> count(n + 1, 0);
  A[0] = 0;
  for (int i = 1; i <= n; i++) {
    (count[i] = count[i - 1]) ^= 1LL << (s[i - 1] -= 'a');
    A[count[i]] = i;
  }
  vector<int> dp(n + 1, E);
  dp[0] = 0;
  for (int i = 0; i < n; i++) {
    for (long long int t = 0; t < 26; t++) {
      long long int to = A[count[i] ^ (1LL << t)];
      if (to <= i) {
        continue;
      }
      dp[to] = min(dp[to], dp[i] + 1);
    }
    long long int to = A[count[i]];
    if (to <= i) {
      continue;
    }
    dp[to] = min(dp[to], dp[i] + 1);
  }
  cout << dp[n] << endl;
  return 0;
}
