#include <bits/stdc++.h>
using namespace std;
string s;
int cs[(1 << 26) + 9], dp[200009];
int main() {
  cin >> s;
  int n = s.size();
  int bit = 0;
  for (int i = 1; i < 1 << 26; i++) cs[i] = -1;
  for (int i = 0; i < n; i++) {
    bit ^= (1 << (s[i] - 97));
    dp[i + 1] = 1012345678;
    if (cs[bit] == -1)
      cs[bit] = i + 1;
    else
      dp[i + 1] = min(dp[i + 1], dp[cs[bit]] + 1);
    for (int j = 0; j < 26; j++) {
      int val = (bit ^ (1 << j));
      if (cs[val] != -1) dp[i + 1] = min(dp[i + 1], dp[cs[val]] + 1);
    }
  }
  cout << dp[n] << endl;
  return 0;
}
