#include <bits/stdc++.h>
using namespace std;
using lli = long long int;
string s;
int cnt[26] = {};
int Count[26] = {};
bool can() {
  int h = 0;
  for (lli i = 0; i < (26); i++) {
    if ((cnt[i] - Count[i]) % 2 == 1) {
      h++;
    }
  }
  return h <= 1;
}
int main() {
  cin >> s;
  int n = s.size();
  for (lli i = 0; i < (n); i++) cnt[s[i] - 'a']++;
  int ans = 0;
  int p = 0;
  while (true) {
    if (can()) {
      ans++;
      break;
    }
    while (p < n) {
      int x = s[p] - 'a';
      if (cnt[x] & 1 and (cnt[x] - Count[x]) % 2 == 1) {
        ans++;
        p++;
        Count[x]++;
        break;
      } else {
        p++;
        Count[x]++;
      }
    }
  }
  cout << ans << endl;
}
