#include <bits/stdc++.h>
using namespace std;
int main() {
  long int dp[67108864];
  int a[200001] = {0}, opt[200001];
  int len;
  char c;
  for (int i = 0; i < 100000000; i++) dp[i] = 100000000;
  for (int i = 0; i < 200001; i++) opt[i] = 100000000;
  for (len = 0; (c = getchar()) != '\n'; len++) {
    a[len + 1] = a[len] ^ (1 << (c - 'a'));
  }
  opt[0] = 0;
  for (int i = 1; i <= len; i++) {
    dp[a[i - 1]] = min(dp[a[i - 1]], (long int)opt[i - 1]);
    opt[i] = dp[a[i] ^ 0];
    for (int x = 1; x < 67108864; x <<= 1) {
      opt[i] = min((long int)opt[i], dp[a[i] ^ x]);
    }
    opt[i]++;
  }
  cout << opt[len] << endl;
  return 0;
}
