#include <bits/stdc++.h>
using namespace std;
int dp[1 << 26 + 1];
int now = 0;
int j;
int main() {
  string S;
  cin >> S;
  for (int _je = sizeof(dp) / sizeof(dp[0]); _je--;) dp[_je] = 1e9;
  dp[0] = 0;
  for (long long i = 0; i < S.size(); ++i) {
    now ^= (1 << (S[i] - 'a'));
    int MIN = 1e9;
    for (j = 1 << 25; j; j >>= 1) {
      MIN = min(MIN, dp[now ^ j]);
    }
    dp[now] = min(dp[now], MIN + 1);
  }
  cout << max(1, dp[now]) << endl;
  return 0;
}
