#include <bits/stdc++.h>
using namespace std;
const int N = 2e5 + 5;
const int INF = 0x3f3f3f3f;
int dp[(1 << 26) + 5];
string s;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cin >> s;
  memset(dp, INF, sizeof(dp));
  dp[0] = 0;
  int mark = 0;
  for (int i = 0; i < s.size(); i++) {
    mark ^= 1 << (s[i] - 'a');
    dp[mark] = dp[mark] + 1;
    for (int j = 0; j < 26; j++)
      dp[mark] = min(dp[mark ^ (1 << j)] + 1, dp[mark]);
  }
  cout << dp[mark] << endl;
  return 0;
}
