#include <bits/stdc++.h>
using namespace std;
string s;
int h[200010];
int dp[1 << 26];
int main() {
  cin >> s;
  int n = s.size();
  for (long long i = (long long)(0); i < (long long)(n); i++) {
    h[i + 1] = h[i] ^ (1LL << (s[i] - 'a'));
  }
  for (long long i = (long long)(0); i < (long long)(1 << 26); i++)
    dp[i] = INT_MAX / 3;
  dp[0] = 0;
  for (long long i = (long long)(0); i < (long long)(n); i++) {
    long long a = INT_MAX / 3;
    for (long long j = (long long)(0); j < (long long)(26); j++) {
      long long tmp = h[i + 1] ^ (1LL << j);
      a = (a < dp[tmp] + 1 ? a : dp[tmp] + 1);
    }
    a = (a < dp[h[i + 1]] + 1 ? a : dp[h[i + 1]] + 1);
    dp[h[i + 1]] = a;
  }
  cout << dp[h[n]] << endl;
  return 0;
}
