#include <bits/stdc++.h>
using namespace std;
const long long MOD = 1000000007;
const long long INF = (long long)1000000007 * 1000000007;
const long double eps = 1e-11;
const long double pi = acos(-1.0);
int sum[200000];
int inv[1 << 26];
int dp[200000];
int main() {
  fill(inv, inv + (1 << 26), -1);
  string s;
  cin >> s;
  int n = s.length();
  int las = 0;
  for (int i = 0; i < n; i++) {
    int t = s[i] - 'a';
    las ^= (1 << t);
    inv[las] = i;
    sum[i] = las;
  }
  fill(dp, dp + n, (int)MOD);
  if (inv[0] >= 0) {
    dp[inv[0]] = 1;
  }
  for (int i = 0; i < 26; i++) {
    if (inv[1 << i] < 0) continue;
    dp[inv[1 << i]] = 1;
  }
  for (int i = 0; i < n; i++) {
    int x = sum[i];
    dp[inv[x]] = min(dp[inv[x]], dp[i] + 1);
    for (int j = 0; j < 26; j++) {
      int y = x ^ (1 << j);
      if (inv[y] < 0) continue;
      dp[inv[y]] = min(dp[inv[y]], dp[i] + 1);
    }
  }
  cout << dp[n - 1] << endl;
  return 0;
}
