#include <bits/stdc++.h>
using namespace std;
char s[200001];
int d[200001];
int cnt[200001];
map<int, int> last;
int main() {
  scanf("%s", s);
  int n;
  for (n = 0; s[n]; n++)
    ;
  for (int i = 1; i <= n; i++) {
    d[i] = 1 << (s[i - 1] - 'a');
    d[i] ^= d[i - 1];
    last[d[i]] = i;
  }
  cnt[0] = 0;
  for (int i = 1; i <= n; i++) cnt[i] = 10000000;
  for (int i = 0; i < n; i++) {
    int t = last[d[i]];
    if (t > i) cnt[t] = min(cnt[t], cnt[i] + 1);
    for (int j = 0; j < 26; j++) {
      int t = last[d[i] ^ (1 << j)];
      if (t > i) cnt[t] = min(cnt[t], cnt[i] + 1);
    }
  }
  printf("%d\n", cnt[n]);
  while (true)
    ;
  return 0;
}
