#include <bits/stdc++.h>
using namespace std;
int dx[8] = {0, 0, -1, 1, 1, 1, -1, -1};
int dy[8] = {-1, 1, 0, 0, 1, -1, 1, -1};
const int SIZE = 200050;
int main() {
  string S;
  cin >> S;
  int sz = S.size();
  int alpha[26] = {};
  int odd = 0;
  for (int i = 0; i < sz; i++) {
    alpha[S[i] - 'a']++;
  }
  for (int i = 0; i < 26; i++) {
    if (alpha[i] % 2) odd++;
  }
  if (odd)
    cout << odd << endl;
  else
    cout << 1 << endl;
  return 0;
}
