#include <bits/stdc++.h>
using namespace std;
int main() {
  string s;
  cin >> s;
  int alp[26][200000] = {};
  for (int i = 0; i < s.length(); i++) {
    for (int j = 0; j < 26; j++) {
      if (j == s[i] - 'a') alp[j][i]++;
      if (!i)
        alp[j][i] += 0;
      else
        alp[j][i] += alp[j][i - 1];
    }
  }
  int cnt = 0, t = s.length() - 1;
  for (int i = 0; i < s.length(); i++) {
    for (int j = s.length() - 1; j >= i; j--) {
      int odd = 0;
      for (int k = 0; k < 26; k++) {
        if ((alp[k][j] - alp[k][i]) % 2) odd++;
      }
      if (odd <= 1) {
        cnt++;
        i = j + 1;
        break;
      }
    }
  }
  cout << cnt << endl;
  return 0;
}
