#include <bits/stdc++.h>
using namespace std;
string s;
long long a[2 * 100000 + 1], opt[2 * 100000], dp[1 << 26], chara['z' - 'a' + 1],
    X['z' - 'a' + 2];
int main() {
  cin >> s;
  for (int i = 0; i < 26; i++) {
    chara[i] = 1 << i;
    X[i + 1] = 1 << i;
  }
  for (int i = 0; i < 1 << 26; i++) dp[i] = INT32_MAX;
  dp[0] = 0;
  for (int i = 0; i < s.length(); i++) opt[i] = INT32_MAX;
  for (int i = 0; i < s.length(); i++) {
    a[i + 1] = a[i] ^ chara[s[i] - 'a'];
  }
  for (int i = 0; i < s.length(); i++) {
    for (int j = 0; j <= 26; j++) {
      opt[i] = min(opt[i], dp[a[i + 1] ^ X[j]] + 1);
    }
    dp[a[i + 1]] = min(dp[a[i + 1]], opt[i]);
  }
  cout << opt[s.length() - 1] << endl;
}
