#include <bits/stdc++.h>
using namespace std;
const double EPS = 1e-10;
const double PI = acos(-1.0);
int main() {
  char s[200010] = {0};
  int n = 0;
  while (cin >> s[n++])
    ;
  n--;
  int a[26] = {0}, b[26] = {0};
  for (int i = (0); i < (n); ++i) {
    a[(int)s[i] - 97]++;
  }
  int cnt = 0;
  int l = 0;
  for (int i = n - 1; i > l; i--) {
    int j = 0;
    for (int k = (0); k < (26); ++k) {
      j += (a[k] & 1);
    }
    if (j == 0 || j == 1) {
      cnt++;
      for (int m = (0); m < (26); ++m) {
        a[m] = b[m];
        b[m] = 0;
      }
      l = i;
      i = n;
    }
    a[((int)s[i]) - 97]--;
    b[((int)s[i]) - 97]++;
  }
  cout << cnt << endl;
  return 0;
}
