#include <bits/stdc++.h>
using namespace std;
const long long INF = 1107110711071107;
long long dp[1 << 26];
signed main() {
  string s;
  long long n, bit = 0;
  cin >> s;
  n = s.size();
  fill_n(dp, 1 << 26, INF);
  dp[0] = 0;
  for (long long i = 0; i < (n); i++) {
    bit ^= 1 << (s[i] - 'a');
    for (long long j = 0; j < (26); j++) {
      dp[bit] = min(dp[bit], dp[bit ^ (1 << j)] + 1);
    }
  }
  cout << max(1LL, dp[bit]) << endl;
  return 0;
}
