#include <bits/stdc++.h>
using namespace std;
long long mod = 1000000007;
long long mod2 = 998244353;
long long mod3 = 1000003;
long long mod4 = 998244853;
long long inf = 1000000000000000000;
double pi = 2 * acos(0);
int dh[4] = {1, -1, 0, 0};
int dw[4] = {0, 0, 1, -1};
int ddh[8] = {-1, -1, -1, 0, 0, 1, 1, 1};
int ddw[8] = {-1, 0, 1, -1, 1, -1, 0, 1};
long long lmax(long long a, long long b) {
  if (a < b)
    return b;
  else
    return a;
}
long long lmin(long long a, long long b) {
  if (a < b)
    return a;
  else
    return b;
}
long long gcd(long long a, long long b) {
  if (a < b) swap(a, b);
  if (b == 0) return a;
  if (a % b == 0) return b;
  return gcd(b, a % b);
}
long long Pow(long long n, long long k) {
  long long ret = 1;
  long long now = n;
  while (k > 0) {
    if (k & 1) ret *= now;
    now *= now;
    k /= 2;
  }
  return ret;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  string s;
  cin >> s;
  unordered_map<int, int> mp, used;
  used[0] = 1;
  mp[0] = 0;
  int now = 0;
  for (long long i = 0; i < s.size(); i++) {
    int t = s[i] - 'a';
    now ^= (1 << t);
    if (used[now] == 1) continue;
    used[now] = 1;
    int mi = 1000000000;
    for (long long j = 0; j < 26; j++) {
      int y = 1 << j;
      if ((now & y) != y) continue;
      int r = now - y;
      if (used[r] == 0) continue;
      mi = min(mi, mp[r]);
    }
    mp[now] = mi + 1;
  }
  mp[0] = 1;
  cout << mp[now] << endl;
}
