#include <bits/stdc++.h>
using namespace std;
int dp[1 << 26];
int main() {
  fill_n(dp, 1 << 26, 1 << 30);
  string s;
  cin >> s;
  int N = s.size();
  int bt = 0;
  dp[0] = 1;
  for (int i = 0; i < 26; i++) dp[1 << i] = 1;
  for (int i = 0; i < N; i++) {
    int x = s[i] - 'a';
    bt ^= 1 << x;
    for (int j = 0; j < 26; j++) dp[bt] = min(dp[bt], dp[bt ^ (1 << j)] + 1);
  }
  cout << dp[bt] << endl;
  return 0;
}
