#include <bits/stdc++.h>
using namespace std;
const long long INF = 1e+9;
const double EPS = 1e-9;
const long long MOD = 1000000007;
const long long dx[] = {1, 0, -1, 0}, dy[] = {0, -1, 0, 1};
long long dp[1 << 26], tmp = 0;
signed main() {
  string s;
  cin >> s;
  for (long long i = 0; i < (1 << 26); i++) dp[i] = INF;
  dp[0] = 0;
  for (long long i = 0; i < s.length(); i++) {
    tmp ^= 1 << (s[i] - 'a');
    for (long long j = 0; j < 26; j++) {
      dp[tmp] = min(dp[tmp], dp[tmp ^ (1 << j)] + 1);
    }
  }
  cout << dp[tmp] << endl;
  return 0;
}
