#include <bits/stdc++.h>
using namespace std;
char ch[200005];
int number[50];
int main() {
  cin >> ch;
  memset(number, 0, sizeof(number));
  int t = strlen(ch);
  int a[50];
  int flag = 0;
  for (int i = 0; i < t; i++) {
    number[ch[i] - 'a']++;
  }
  for (int i = 0; i < 50; i++) {
    if (number[i]) a[flag++] = number[i];
  }
  int sum = 0;
  int ok = 1;
  for (int i = 0; i < flag; i++) {
    if (a[i] >= 2) ok = 1;
    a[i] %= 2;
  }
  if (ok) sum++;
  int tt = 0;
  for (int i = 0; i < flag; i++) {
    if (a[i]) tt++;
  }
  if (tt)
    cout << tt << endl;
  else
    cout << sum << endl;
  return 0;
}
