#include <bits/stdc++.h>
using namespace std;
const int N = (1 << 26) + 10;
string s;
int n, ans, a[N];
int main() {
  cin >> s;
  n = s.size();
  s = " " + s;
  int now = 0;
  a[0] = 1;
  ans = 2e9;
  for (register int i = 1; i <= n; i++) {
    now = now ^ (1 << (s[i] - 'a'));
    int tmp = 2e9;
    if (a[now]) tmp = a[now];
    for (register int j = 0; j <= 25; j++) {
      int tmp = now ^ (1 << j);
      if (a[tmp]) tmp = min(tmp, a[tmp]);
    }
    if (i == n) ans = tmp + 1;
    if (!a[now])
      a[now] = tmp + 1;
    else
      a[now] = min(a[now], tmp + 1);
  }
  cout << ans - 1;
  return 0;
}
