#include <bits/stdc++.h>
using namespace std;
const long long e5 = 1 << 21;
const long long mod = 1000000007;
const long long e3 = 1 << 13;
const long long INF = 1ll << 62;
string s;
long long dp[1 << 26];
int main() {
  cin >> s;
  long long bit = 0;
  fill(dp, dp + (1 << 26), INF);
  dp[0] = 0;
  for (char c : s) {
    bit ^= (1 << c - 'a');
    long long m = INF;
    for (long long i = 0; i < 26; i++) {
      m = min(m, dp[(bit ^ (1 << i))]);
    }
    dp[bit] = min(dp[bit], m + 1);
  }
  cout << max(1ll, dp[bit]) << endl;
}
