#include <bits/stdc++.h>
using namespace std;
const int MAX = 2e5 + 10;
const int INF = 2e9;
string S;
int h[MAX];
int dp[1 << 27];
long long solve() {
  int x = 0;
  for (long long i = 0; i < S.size(); ++i) h[i] = (x ^= 1 << (S[i] - 'a'));
  for (long long i = 0; i < 1 << 27; ++i) dp[i] = INF;
  dp[0] = 1;
  for (long long i = 0; i < 27; ++i) dp[1 << i] = 1;
  for (long long i = 0; i < S.size(); ++i) {
    for (long long j = 0; j < 26; ++j)
      dp[h[i]] = min(dp[h[i]], dp[h[i] ^ (1 << j)] + 1);
  }
  return dp[h[S.size() - 1]];
}
int main() {
  cin >> S;
  cout << solve() << endl;
}
