#include <bits/stdc++.h>
using namespace std;
int DP[210000] = {};
int m[(1 << 26)] = {};
int main() {
  string str;
  cin >> str;
  int num = 0;
  DP[0] = 0;
  m[0] = 1;
  for (int i = 0; i < str.size(); i++) {
    DP[i + 1] = 10000000;
    num = (num ^ (1 << (str[i] - 'a')));
    if (m[num] == 0) {
      m[num] = i + 2;
    } else {
      DP[i + 1] = min(DP[i + 1], DP[m[num] - 1] + 1);
    }
    for (int j = 0; j < 26; j++) {
      int state = (num ^ (1 << j));
      if (m[state] != 0) {
        DP[i + 1] = min(DP[i + 1], DP[m[state] - 1] + 1);
      }
    }
  }
  for (int i = 0; i <= str.size(); i++) {
  }
  cout << DP[str.size()] << endl;
  return 0;
}
