#include <bits/stdc++.h>
using namespace std;
char st[100100];
int dp[(1 << 26) + 10];
int pre[100100];
int main() {
  scanf("%s", st + 1);
  int len = strlen(st + 1), ans = 0x3f3f3f3f;
  memset(dp, 0x3f, sizeof(dp));
  dp[0] = 0;
  for (int i = 1; i <= len; i++) {
    pre[i] = pre[i - 1] ^ (1 << (st[i] - 'a'));
    for (int j = 0; j < 26; j++) {
      int sta = pre[i] ^ (1 << j);
      dp[pre[i]] = min(dp[pre[i]], dp[sta] + 1);
    }
  }
  printf("%d\n", max(dp[pre[len]], 1));
}
