#include <bits/stdc++.h>
using namespace std;
template <class T, class U>
inline void Max(T &a, U b) {
  if (a < b) a = b;
}
template <class T, class U>
inline void Min(T &a, U b) {
  if (a > b) a = b;
}
int cnt[200005][26];
int p(char c) { return c - 'a'; }
bool ok(int i, int end) {
  int num_odd = 0;
  for (int c = 'a'; c <= 'z'; ++c) {
    if ((cnt[end][p(c)] - cnt[i][p(c)]) % 2) num_odd++;
    if (num_odd > 1) return false;
  }
  return true;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  string s;
  cin >> s;
  int n = s.length();
  for (int i = 0; i < n; ++i) {
    for (int c = 'a'; c <= 'z'; ++c) {
      if (c == s[i])
        cnt[i + 1][p(c)] = 1 + cnt[i][p(c)];
      else
        cnt[i + 1][p(c)] = cnt[i][p(c)];
    }
  }
  int end = n;
  int res = 0;
  while (end > 0) {
    for (int i = 0; i < end; ++i) {
      if (ok(i, end)) {
        res++;
        end = i;
        break;
      }
    }
  }
  cout << res << endl;
}
