#include <bits/stdc++.h>
using namespace std;
using LL = long long;
string S;
int N;
int main(void) {
  cin >> S;
  N = S.size();
  map<char, int> mp;
  for (char c : S) {
    mp[c]++;
  }
  int ans = 0;
  for (auto p : mp) {
    if (p.second % 2) {
      ++ans;
    }
  }
  cout << max(ans, 1) << endl;
  return 0;
}
