#include <bits/stdc++.h>
using namespace std;
int op[100005], a[100005], str[30];
int dp[1 << 26];
int main() {
  string s;
  int n;
  cin >> s;
  n = s.size();
  memset(str, 0, sizeof(str));
  for (int i = 0; i < n; i++) {
    int bit = 0;
    str[s[i] - 'a']++;
    for (int j = 0; j < 26; j++) {
      if (str[j] % 2) {
        bit += (1 << j);
      }
    }
    a[i + 1] = bit;
  }
  for (int i = 0; i < 1 << 26; i++) {
    dp[i] = 999999;
  }
  for (int i = 0; i <= n; i++) op[i] = 999999;
  dp[0] = 0;
  for (int i = 1; i <= n; i++) {
    op[i] = min(op[i], dp[a[i]] + 1);
    for (int j = 0; j < 26; j++) {
      op[i] = min(op[i], dp[a[i] ^ (1 << j)] + 1);
    }
    dp[a[i]] = min(dp[a[i]], op[i]);
  }
  cout << op[n] << endl;
  return 0;
}
