#include <bits/stdc++.h>
using namespace std;
int dp;
map<long long, int> dp2;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  string s;
  cin >> s;
  int N = s.length();
  long long x = 0;
  dp = 0;
  dp2[0] = 0;
  for (int i = (0); i < (N); ++i) {
    x ^= 1LL << (s[i] - 'a');
    if (!dp2.count(x)) dp2[x] = 1e9;
    int ma = min((int)1e9, dp2[x]);
    for (int j = (0); j < (26); ++j) {
      long long y = x ^ (1LL << j);
      if (!dp2.count(y)) dp2[y] = 1e9;
      ma = min(ma, dp2[y]);
    }
    dp2[x] = min(dp2[x], ma + 1);
    dp = ma + 1;
  }
  cout << dp << endl;
  return 0;
}
