#include <bits/stdc++.h>
using namespace std;
struct st {
  int pos, pre, val;
};
char s[200002];
int lst[1 << 26];
queue<st> q;
void in(int pre, int pos, int val) {
  if (lst[pre] > pos) {
    q.push({lst[pre], pre, val + 1});
    lst[pre] = 0;
  }
}
int main() {
  scanf("%s", s + 1);
  int L = strlen(s + 1);
  for (int v = 0, i = 1; i <= L; i++) {
    v ^= (1 << (s[i] - 'a'));
    lst[v] = i;
  }
  int ans = 0;
  in(0, 0, 0);
  for (int i = 0; i < 26; i++) in(1 << i, 0, 0);
  while (!q.empty()) {
    st now = q.front();
    q.pop();
    if (now.pos == L) {
      ans = now.val;
      break;
    }
    for (int i = 0; i < 26; i++) {
      in(now.pre ^ (1 << i), now.pos, now.val);
    }
  }
  printf("%d\n", ans);
  return 0;
}
