#include <bits/stdc++.h>
using namespace std;
string s;
int dp[(1 << 27) + 1];
long long now = 0;
int main() {
  cin >> s;
  memset(dp, 63, sizeof(dp));
  dp[0] = 0;
  for (int i = 0; i <= s.length() - 1; i++) {
    now ^= (1 << (s[i] - 'a' + 1));
    for (int j = 1; j <= 26; j++) {
      if ((now ^ (1 << j)) != now) {
        dp[now] = min(dp[now], dp[now ^ (1 << j)] + 1);
      }
    }
  }
  cout << max(1, dp[now]) << endl;
  return 0;
}
