#include <bits/stdc++.h>
using namespace std;
const int MAXN = (int)2e5 + 5;
char str[MAXN];
int mark[MAXN], dp[(1 << 26) + 10];
int main() {
  int n;
  scanf("%s", str + 1);
  n = strlen(str + 1);
  memset(dp, -1, sizeof(dp));
  dp[0] = 0;
  for (int i = 1; i <= n; i++) {
    mark[i] = (mark[i - 1] ^ (1 << (str[i] - 'a')));
    for (int j = 0; j < 26; j++) {
      int tmp = dp[mark[i] ^ (1 << j)] + 1;
      if (dp[mark[i]] == -1 || dp[mark[i]] > tmp) dp[mark[i]] = tmp;
    }
  }
  dp[0] = 1;
  printf("%d\n", dp[mark[n]]);
  return 0;
}
