#include <bits/stdc++.h>
using namespace std;
int dp[(1 << 26)];
string s;
int main() {
  cin >> s;
  int n = s.size();
  for (int i = 0; i < (1 << 26); i++) dp[i] = 1000000000;
  dp[0] = 0;
  int cur = 0;
  for (int i = 0; i < s.size(); i++) {
    cur ^= (1 << (s[i] - 'a'));
    int v = dp[cur] + 1;
    for (int j = 0; j < 26; j++) {
      int cur2 = cur ^ (1 << j);
      v = min(v, dp[cur2] + 1);
    }
    dp[cur] = v;
  }
  cout << dp[cur] << endl;
}
