#include <bits/stdc++.h>
using namespace std;
const int N = 200000 + 10;
int dp[N], cnt[N];
int main() {
  string s;
  cin >> s;
  int ans = 0;
  for (int i = 0; i < s.size(); i++) cnt[s[i] - 'a']++;
  for (int i = 0; i < 26; i++) {
    if (cnt[i] & 1) ans++;
  }
  if (ans)
    cout << ans << endl;
  else
    cout << 1 << endl;
  return 0;
}
