#include <bits/stdc++.h>
using namespace std;
int n, i, j, f[1 << 27], ans, c[212345];
string s;
int main() {
  cin >> s;
  s = " " + s;
  n = s.size();
  for (i = 1; i < n; i++) {
    c[i] = c[i - 1] ^ (1 << (s[i] - 'a'));
  }
  if (!c[n - 1]) {
    cout << "1\n";
    return 0;
  }
  memset(f, 50, sizeof(f));
  f[0] = 0;
  for (i = 1; i < n; i++) {
    ans = n + n + n + n + 345;
    for (j = 0; j < 26; j++) {
      ans = min(ans, f[c[i] ^ (1 << j)] + 1);
    }
    f[c[i]] = min(f[c[i]], ans);
  }
  cout << f[c[n - 1]] << endl;
  return 0;
}
