#include <bits/stdc++.h>
using namespace std;
const int N = 2e5 + 5;
char s[N];
int dp[1 << 26];
int main() {
  memset(dp, 0x3f3f3f3f, sizeof(dp));
  scanf("%s", s + 1);
  int n = strlen(s + 1);
  dp[0] = 0;
  int st = 0;
  for (int i = 1; i <= n; i++) {
    st ^= 1 << s[i] - 'a';
    dp[st]++;
    if (__builtin_popcount(st) <= 1) dp[st] = 1;
    for (int j = 0; j < 26; j++)
      if (st >> j & 1) dp[st] = min(dp[st], dp[st ^ (1 << j)] + 1);
  }
  printf("%d\n", dp[st]);
}
