#include <bits/stdc++.h>
using namespace std;
int dp[(1 << 27) + 1];
char s[(int)2e5 + 2];
int main() {
  scanf("%s", s);
  int n = strlen(s);
  memset(dp, 0x7f7f7f, sizeof(dp));
  long long now = 0;
  dp[now] = 0;
  for (int i = 0; i < n; i++) {
    now ^= (1 << (s[i] - 'a'));
    for (int j = 0; j <= 25; j++)
      if ((now ^ (1 << j)) != now)
        dp[now] = min(dp[now], dp[now ^ (1 << j)] + 1);
  }
  if (now == 0) dp[now] = 1;
  printf("%d\n", dp[now]);
}
