#include <bits/stdc++.h>
using namespace std;
const int N = 1 << 26;
string s;
int dp[N + 10];
int main() {
  cin >> s;
  int have = 0;
  for (int i = 0; i < (1 << 26); i++) dp[i] = 1e6;
  for (auto i : s) {
    have ^= 1 << (i - 'a');
    dp[1 << (i - 'a')] = 1;
    if (!(have & (have - 1))) dp[have] = 1;
    for (int j = 0; j < 26; j++)
      dp[have] = min(dp[have], dp[1 << j] + dp[have ^ (1 << j)]);
  }
  cout << dp[have] << endl;
}
