#include <bits/stdc++.h>
using namespace std;
int times[68000000];
int main() {
  string s;
  cin >> s;
  for (int i = 0; i < 68000000; i++) times[i] = 30;
  int m = 0;
  times[0] = 0;
  for (int i = 0; i < s.size(); i++) {
    m = m ^ (1 << (s[i] - 'a'));
    int p = times[m];
    for (int k = 0; k < 26; k++) p = min(p, times[m ^ (1 << k)]);
    times[m] = min(times[m], p + 1);
  }
  if (times[m] == 0)
    printf("1");
  else
    printf("%d", times[m]);
  printf("\n");
  return 0;
}
