#include <bits/stdc++.h>
using namespace std;
bool check_Palindrome(char *s) {
  int flag = 0;
  for (int i = 0; s[i] != '\0'; i++) {
    flag ^= 1 << (s[i] - 'a');
  }
  return __builtin_popcount(flag) <= 1;
}
int pos[1 << 26];
int memo[200010];
int dp[1 << 26];
int main() {
  char s[200010];
  int n = 0;
  scanf("%s", s);
  n = strlen(s);
  assert(n < 200010);
  if (check_Palindrome(s)) {
    printf("%d\n", 1);
    return 0;
  }
  for (int i = 0; i < (1 << 26); i++) {
    pos[i] = -1;
    dp[i] = 1000000000;
  }
  dp[0] = 0;
  int flag = 0;
  for (int i = 0; i < n; i++) {
    flag ^= 1 << (s[i] - 'a');
    pos[flag] = i + 1;
    memo[i + 1] = flag;
  }
  memo[0] = 0;
  dp[0] = 0;
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < 26; j++) {
      int next = memo[i] ^ (1 << j);
      assert(next < (1 << 26));
      if (pos[next] > i) {
        dp[next] = min(dp[memo[i]] + 1, dp[next]);
      }
    }
  }
  printf("%d\n", dp[memo[n]]);
  return 0;
}
