#include <bits/stdc++.h>
using namespace std;
string s;
int cn[26];
int main(int argc, char const *argv[]) {
  memset(cn, 0, sizeof(cn));
  cin >> s;
  for (const char it : s) {
    cn[it - 'a']++;
  }
  int take = 0;
  for (int i = 0; i < 26; i++) {
    if (cn[i] & 1) {
      take++;
    }
  }
  if (take == 0)
    cout << take + 1 << "\n";
  else
    cout << take << "\n";
  return 0;
}
