#include <bits/stdc++.h>
using namespace std;
char s[210000];
short ma[1 << 26];
int used[1 << 26];
int main() {
  int i, l, now, tmp, bma, btmp, ans, j, x, y;
  vector<int> q;
  scanf("%s", s);
  l = strlen(s);
  now = 0;
  memset(ma, 0, sizeof(ma));
  ma[0] = 1;
  for (i = 0; i < l; i++) {
    now ^= (1 << (s[i] - 'a'));
    ma[now] = 1;
  }
  if (now == 0) {
    ans = 1;
  } else {
    q.clear();
    q.push_back(0);
    memset(used, -1, sizeof(used));
    used[0] = 0;
    for (i = 0; i < q.size(); i++) {
      x = q[i];
      for (j = 0; j < 26; j++) {
        y = (x ^ (1 << j));
        if ((used[y] == -1) && (ma[y] != 0)) {
          used[y] = used[x] + 1;
          q.push_back(y);
        }
      }
    }
    ans = used[now];
  }
  printf("%d\n", ans);
  return 0;
}
