#include <bits/stdc++.h>
using namespace std;
const int maxn = 2e5 + 1;
string s;
int n, f, d[maxn], id[(1 << 27)];
void OpenFile() {}
void Enter() {
  cin >> s;
  n = s.size();
  s = ' ' + s;
}
void Init() {}
void Solve() {
  fill(id, id + (1 << 26), -1);
  id[0] = 0;
  d[0] = 0;
  for (int i = 1; i <= n; ++i) {
    f ^= 1 << (s[i] - 'a');
    if (id[f] != -1)
      d[i] = d[id[f]] + 1;
    else
      d[i] = n;
    for (int j = 0; j < 26; ++j) {
      if (id[f ^ (1 << j)] != -1) {
        d[i] = min(d[i], d[id[f ^ (1 << j)]] + 1);
      }
    }
    if (id[f] == -1) id[f] = i;
  }
  cout << d[n];
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  Enter();
  Init();
  Solve();
}
