#include <bits/stdc++.h>
using namespace std;
template <typename T>
void chmax(T &a, T b) {
  a = max(a, b);
}
template <typename T>
void chmin(T &a, T b) {
  a = min(a, b);
}
template <typename T>
void chadd(T &a, T b) {
  a = a + b;
}
long long int dx[] = {0, 0, 1, -1};
long long int dy[] = {1, -1, 0, 0};
constexpr long long INF = 1001001001001001LL;
constexpr long long MOD = 1000000007LL;
long long int cnt[200010][26];
signed main() {
  string s;
  cin >> s;
  long long int len = s.length();
  for (long long int(i) = (0); (i) < (len); (i)++) {
    for (long long int(j) = (0); (j) < (26); (j)++) cnt[i + 1][j] += cnt[i][j];
    (cnt[i + 1][s[i] - 'a'] += 1) %= 2;
  }
  long long int p = len, ans = 0;
  while (p != 0) {
    long long int mi = INF;
    for (long long int(i) = (p); (i) >= (0); (i)--) {
      long long int temp = 0;
      for (long long int(j) = (0); (j) < (26); (j)++)
        temp += (cnt[p][j] - cnt[i][j] + 2) % 2;
      if (temp <= 1) chmin(mi, i);
    }
    p = mi;
    ans++;
  }
  cout << ans << endl;
  return 0;
}
