#include <bits/stdc++.h>
using namespace std;
const int INF = 1 << 28;
const long long LLINF = 1LL << 60;
const double EPS = 1e-9;
int dp[1 << 26];
int range[1 << 26];
int main() {
  int bit = 0;
  string S;
  cin >> S;
  for (int i = 0; i < S.size(); i++) {
    int nbit = bit ^ (1 << (S[i] - 'a'));
    range[bit] = nbit;
    bit = nbit;
  }
  int val = 0, cnt = 0;
  while (val != bit) {
    val = range[val];
    cnt++;
  }
  cout << cnt + (cnt == 0) << endl;
  return (0);
}
