#include <bits/stdc++.h>
using namespace std;
map<int, vector<int> > a;
int main() {
  string s;
  cin >> s;
  int n = s.size();
  int tmp = 0;
  for (int i = 0; i < (int)(n); i++) {
    int c = s[i] - 'a';
    tmp ^= (1 << c);
    a[tmp].push_back(i + 1);
  }
  int bits = 0;
  int id = 0;
  int res = 1;
  while (1) {
    int mx = -1;
    int mxbits = 0;
    int yy = a[bits].size();
    if (yy != 0 && a[bits][yy - 1] > id) {
      if (mx < a[bits][yy - 1]) {
        mx = a[bits][yy - 1];
        mxbits = bits;
      }
    }
    for (int i = 0; i < (int)(26); i++) {
      int k = bits ^ (1 << i);
      if (a.find(k) == a.end()) continue;
      int xx = a[k].size();
      if (xx != 0 && a[k][xx - 1] > id) {
        if (mx < a[k][xx - 1]) {
          mx = a[k][xx - 1];
          mxbits = k;
        }
      }
    }
    if (mx == n) break;
    res++;
    bits = mxbits;
    id = mx;
  }
  cout << res << endl;
  return 0;
}
