#include <bits/stdc++.h>
using namespace std;
int f[(1 << 26) + 10];
const int oo = 1e9;
int main() {
  for (int i = 0; i < (1 << 26); i++) f[i] = oo;
  string s;
  cin >> s;
  int h = 0, fi;
  f[0] = 0;
  for (char ch : s) {
    h ^= (1 << (ch - 'a'));
    fi = 1 + f[h];
    for (int i = 0; i < 26; i++) {
      int m = (h ^ (1 << i));
      fi = min(fi, 1 + f[m]);
    }
    f[h] = min(f[h], fi);
  }
  printf("%d\n", fi);
  return 0;
}
