#include <bits/stdc++.h>
using namespace std;
const int maxn = 2e5 + 1;
string s;
int n, f[(1 << 26)], x;
void OpenFile() {}
void Enter() { cin >> s; }
void Init() {}
void Solve() {
  fill(f + 1, f + (1 << 26), s.size());
  for (auto c : s) {
    x ^= 1 << (c - 'a');
    for (int i = 0; i < 26; ++i) f[x] = min(f[x], f[x ^ (1 << i)] + 1);
  }
  cout << f[x];
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  Enter();
  Init();
  Solve();
}
