#include <bits/stdc++.h>
using namespace std;
int main() {
  string s;
  cin >> s;
  int al[27] = {0};
  for (int i = 0; i < int(s.size()); i++) {
    al[s[i] - 'a']++;
  }
  int cnt = 0;
  for (int i = 0; i < int(27); i++) cnt += al[i] % 2;
  printf("%d\n", max(1, cnt));
}
