#include <bits/stdc++.h>
using namespace std;
int dp[1 << 26];
int main() {
  string s;
  cin >> s;
  int now = 0;
  fill(dp, dp + (1 << 26), 1000000000);
  dp[0] = 0;
  for (int i = 0; i < s.size(); i++) {
    now ^= (1 << (s[i] - 'a'));
    for (int j = 0; j < 26; j++) dp[now] = min(dp[now], dp[now ^ (1 << j)] + 1);
  }
  printf("%d\n", dp[now]);
}
