#include <bits/stdc++.h>
using namespace std;
const int N = 200100, M = 31;
int n, ans, a[M];
char s[N];
int main() {
  scanf("%s", &s[1]);
  n = strlen(s + 1);
  for (int i = 1; i <= n; ++i) a[s[i] - 'a' + 1]++;
  for (int i = 1; i <= 26; ++i)
    if (a[i] % 2) ans++;
  if (!ans) ans = 1;
  printf("%d", ans);
  return 0;
}
