#include <bits/stdc++.h>
using namespace std;
int dp[1 << 26];
int main() {
  string s;
  cin >> s;
  int x = 0;
  memset(dp, 1e9, sizeof(dp));
  dp[0] = 0;
  int ans = 1e9;
  for (int i = 0; i < s.size(); i++) {
    ans = 1e9;
    x ^= 1 << (s[i] - 'a');
    ans = min(ans, dp[x] + 1);
    for (int j = 0; j < 26; j++) ans = min(ans, dp[x ^ (1 << j)] + 1);
    dp[x] = min(dp[x], ans);
  }
  cout << ans << endl;
  return 0;
}
