#include <bits/stdc++.h>
using namespace std;
const int maxn = 2e5 + 100;
char str[maxn];
int a[maxn];
int dp[(1 << 27)];
int main() {
  cin >> str;
  int L = strlen(str), ans = 0;
  for (int i = 0; i < L; i++) {
    ans ^= (1 << (str[i] - 'a'));
    a[i] = ans;
  }
  memset(dp, 1, sizeof(dp));
  dp[0] = 0;
  for (int i = 0; i < L; i++) {
    for (int j = 0; j < 26; j++)
      dp[a[i]] = min(dp[a[i] ^ (1 << j)] + 1, dp[a[i]]);
  }
  cout << dp[a[L - 1]] << endl;
  return 0;
}
