#include <bits/stdc++.h>
using namespace std;
int vx[] = {0, 1, 0, -1};
int vy[] = {1, 0, -1, 0};
int dx[] = {0, 1, 0, -1, 1, 1, -1, -1};
int dy[] = {1, 0, -1, 0, 1, -1, 1, -1};
const long long mod = 1000000000 + 7;
const int MAX_N = 1000;
int main() {
  string s;
  cin >> s;
  int num[26];
  int ans = 0;
  fill(num, num + 26, 0);
  for (int i = 0; i < s.size(); i++) {
    num[s[i] - 'a']++;
  }
  for (int i = 0; i < 26; i++) {
    if (num[i] % 2 != 0) {
      ans++;
    }
  }
  if (ans == 0) ans = 1;
  cout << ans << endl;
  return 0;
}
