#include <bits/stdc++.h>
using namespace std;
int n, tag, f[200010];
char s[200010];
unordered_map<int, int> mp;
int main() {
  scanf("%s", s);
  n = strlen(s);
  f[0] = 0;
  tag = 0;
  mp[0] = 0;
  for (int i = 1; i <= n; ++i) {
    f[i] = 1e9;
    tag ^= 1 << (s[i - 1] - 'a');
    for (int j = 0; j < 26; ++j) {
      int x = tag ^ (1 << j);
      if (mp.find(x) != mp.end()) f[i] = min(f[i], mp[x] + 1);
    }
    if (mp.find(tag) != mp.end())
      f[i] = min(f[i], mp[tag] + 1);
    else
      mp[tag] = f[i];
  }
  printf("%d\n", f[n]);
  return 0;
}
