#include <bits/stdc++.h>
using namespace std;
const int MAX_N = (1 << 26);
int dp[MAX_N];
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  string s;
  cin >> s;
  memset(dp, 0x3f, sizeof(dp));
  dp[0] = 0;
  int kp = 0;
  for (int i = 0; i < (int)((int)(s).size()); ++i) {
    kp ^= (1 << (s[i] - 'a'));
    dp[kp] = min(dp[kp], dp[kp] + 1);
    for (int j = 0; j < (int)(26); ++j)
      dp[kp] = min(dp[kp], dp[kp ^ (1 << j)] + 1);
  }
  cout << dp[kp] << "\n";
  return 0;
}
