#include <bits/stdc++.h>
using namespace std;
const int INF = 1e9;
const long long MOD = 1e9 + 7;
double EPS = 1e-8;
int main() {
  string s;
  cin >> s;
  map<char, int> mp;
  int n = s.size();
  for (int i = (0); i < (int)(n); i++) mp[s[i]]++;
  int odd = 0;
  for (auto& p : mp) odd += p.second & 1;
  cout << max(1, odd) << endl;
  return 0;
}
