#include <bits/stdc++.h>
using namespace std;
const int MAX_N = (1 << 26);
int a[MAX_N];
int kp[200005], dp[200005];
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  string s;
  cin >> s;
  memset(a, -1, sizeof(a));
  kp[0] = 0;
  a[kp[0]] = 0;
  for (int i = 0; i < (int)((int)(s).size()); ++i) {
    kp[i + 1] = (kp[i] ^ (1 << (s[i] - 'a')));
    a[kp[i + 1]] = i + 1;
  }
  for (int i = 0; i < (int)((int)(s).size() + 1); ++i) {
    dp[i] = 1000000005;
  }
  dp[0] = 0;
  for (int i = 0; i < (int)((int)(s).size()); ++i) {
    if (dp[i] != 1000000005) {
      if (a[kp[i]] >= 0) dp[a[kp[i]]] = min(dp[a[kp[i]]], dp[i] + 1);
      for (int j = 0; j < (int)(26); ++j) {
        if (a[kp[i] ^ (1 << j)] >= 0)
          dp[a[kp[i] ^ (1 << j)]] = min(dp[a[kp[i] ^ (1 << j)]], dp[i] + 1);
      }
    }
  }
  cout << dp[(int)(s).size()] << "\n";
  return 0;
}
