#include <bits/stdc++.h>
using namespace std;
map<int, int> dp;
int main() {
  ios::sync_with_stdio(0);
  string s;
  cin >> s;
  dp[0] = 0;
  int n = (int)(s).size();
  int b = 0;
  for (int i = (0); i < int(n); ++i) {
    int ind = s[i] - 'a';
    b ^= (1 << ind);
    dp[b] = n;
    for (int j = (0); j < int(28); ++j) {
      int c = b ^ (1 << j);
      if (!dp.count(c)) continue;
      dp[b] = min(dp[b], dp[c] + 1);
    }
  }
  int num = dp[b];
  if (num == 0)
    cout << 1 << endl;
  else
    cout << num << endl;
}
