#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using P = pair<int, int>;
constexpr ld EPS = 1e-12;
constexpr int INF = numeric_limits<int>::max() / 2;
constexpr int MOD = 1e9 + 7;
vector<int> dp(1 << 26, INF);
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  string s;
  cin >> s;
  int n = s.length();
  ll mask = 0;
  dp[0] = 0;
  for (int i = 0; i < n; i++) {
    int b = s[i] - 'a';
    mask ^= (1LL << b);
    for (int j = 0; j < 26; j++) {
      if ((mask >> j) & 1) {
        dp[mask] = min(dp[mask], dp[mask ^ (1 << j)] + 1);
      }
    }
  }
  cout << max(1, dp[mask]) << endl;
}
