#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);
  for (int i = 1; i <= (1 << 26); i++) dp[i] = (int)1e9;
  for (int i = 1; i <= n; i++) {
    mark[i] = (mark[i - 1] ^ (1 << (str[i] - 'a')));
    for (int j = 0; j < 26; j++) {
      dp[mark[i]] = min(dp[mark[i] ^ (1 << j)] + 1, dp[mark[i]]);
    }
  }
  printf("%d\n", dp[mark[n]]);
  return 0;
}
