#include <bits/stdc++.h>
constexpr int X = 26;
constexpr int INF = 1 << 30;
void solve() {
  std::string s;
  std::cin >> s;
  int x = 0;
  std::vector<int> dist(1 << X, INF);
  dist[x] = 0;
  for (char c : s) {
    int d = c - 'a';
    x ^= (1 << d);
    if (dist[x] < INF) continue;
    for (int i = 0; i < X; ++i) {
      dist[x] = std::min(dist[x], dist[x ^ (1 << i)] + 1);
    }
  }
  if (x == 0) {
    std::cout << 1 << std::endl;
    return;
  }
  std::cout << (x == 0 ? 1 : dist[x]) << std::endl;
}
int main() {
  std::cin.tie(nullptr);
  std::cout.tie(nullptr);
  std::ios::sync_with_stdio(false);
  solve();
  return 0;
}
