#include <bits/stdc++.h>
using namespace std;
const long long mod = 1e9 + 7;
const long long inf = 1LL << 61;
int main() {
  string s;
  cin >> s;
  vector<long long> dp(1 << 26, inf);
  dp[0] = 0;
  long long x = 0;
  for (char c : s) {
    x ^= 1 << (c - 'a');
    for (long long i = 0; i < 26; i++) dp[x] = min(dp[x], dp[x ^ (1 << i)] + 1);
  }
  cout << max(1LL, dp[x]) << endl;
}
