#include <bits/stdc++.h>
using namespace std;
int cnt[32];
bool isKaibun() {
  bool flag = false;
  for (int i = 0; i <= 26; i++) {
    if (cnt[i] % 2 == 0)
      continue;
    else if (flag)
      return false;
    else
      flag = true;
  }
  return true;
}
int main(void) {
  string s;
  cin >> s;
  int ans = 0;
  int lastOK = -1;
  for (;;) {
    int i = lastOK + 1;
    for (; i < s.size(); i++) {
      cnt[s[i] - 'a']++;
      if (isKaibun()) lastOK = i;
    }
    ans++;
    for (int j = 0; j < 32; j++) cnt[j] = 0;
    if (lastOK == s.size() - 1) break;
  }
  cout << ans << endl;
}
