#include <bits/stdc++.h>
using namespace std;
const int inf = 1000000001;
const long long INF = 1e18;
int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};
int dx2[8] = {1, 1, 0, -1, -1, -1, 0, 1}, dy2[8] = {0, 1, 1, 1, 0, -1, -1, -1};
int main() {
  string s;
  cin >> s;
  int n = s.size(), i, j;
  vector<long long> sum(n + 1);
  for (i = 0; i < n; i++) {
    sum[i + 1] = sum[i] ^ (1 << (s[i] - 'a'));
  }
  vector<long long> x(27);
  x[1] = 1;
  for (i = 1; i < 26; i++) {
    x[i + 1] = 2 * x[i];
  }
  vector<int> dp((1 << 27) - 1, inf);
  dp[0] = 0;
  for (i = 1; i <= n; i++) {
    int m = inf + 2;
    for (j = 0; j < 27; j++) {
      m = min(m, dp[x[j] ^ sum[i]]);
    }
    dp[sum[i]] = min(dp[sum[i]], m + 1);
  }
  cout << dp[sum[n]] << endl;
}
