#include <bits/stdc++.h>
using namespace std;
const int magic = 27, N = (1 << magic) + 5;
int dp[N], res[200005];
int main() {
  int n;
  string s;
  cin >> s;
  n = s.size();
  s = "#" + s;
  for (int i = 0; i < N; i++) {
    dp[i] = n + 10;
  }
  dp[0] = 0;
  int cur = 0;
  for (int i = 1; i <= n; i++) {
    int bit = s[i] - 'a';
    cur ^= (1 << bit);
    res[i] = dp[cur] + 1;
    for (int j = 0; j < 26; j++) {
      if (((cur >> j) & 1) == 0) continue;
      int nw = cur ^ (1 << j);
      res[i] = min(res[i], dp[nw] + 1);
    }
    dp[cur] = min(dp[cur], res[i]);
  }
  cout << res[n] << endl;
}
