#include <bits/stdc++.h>
using namespace std;
const int N = 200010;
const int INF = 1e9;
int n;
int f[(1 << 26) + 10];
char s[N];
int main() {
  scanf("%s", s + 1);
  n = strlen(s + 1);
  for (int i = 0; i < 1 << 26; i++) {
    if (__builtin_popcount(i) <= 1)
      f[i] = 1;
    else
      f[i] = INF;
  }
  int st = 0, lst;
  for (int i = 1; i <= n; i++) {
    lst = st;
    st ^= 1 << s[i] - 'a';
    f[st] = min(f[st], f[lst] + 1);
  }
  printf("%d\n", f[st]);
  return 0;
}
