#include <bits/stdc++.h>
using namespace std;
template <class t>
long long int gcd(t g, t h) {
  return (h == 0 ? g : gcd(h, g % h));
}
struct Comp {
  bool operator()(const std::pair<int, int> &a, const std::pair<int, int> &b) {
    if (a.first != b.first) {
      return a.first < b.first;
    }
    return a.second > b.second;
  }
} comp_functor;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  long long int p, i, j, ans = 0, c = 0, a[300005], n, f = 0, o = 0, x, temp,
                         l = 0, r = 0, h[26] = {0};
  string s;
  cin >> s;
  n = s.length();
  for (i = 0; i < n; i++) {
    h[s[i] - 'a']++;
  }
  for (i = 0; i < 26; i++) {
    if (h[i] % 2 != 0) {
      o++;
    }
  }
  if (o == 1 || o == 0) {
    cout << "1";
  } else {
    cout << o;
  }
  return 0;
}
