#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<int, int>;
const int mod = 1e9 + 7, INF = 1 << 30;
const double EPS = 1e-12, PI = 3.1415926535897932384626;
const ll LINF = 1LL << 60;
const int MAX_N = 200005;
const ll lmod = 1e9 + 7;
int dp[1 << 26];
int a[MAX_N];
int C = 26;
string S;
int main() {
  cin >> S;
  int N = S.size();
  for (int i = 0; i < N; i++) {
    int b = S[i] - 'a';
    a[i + 1] = a[i] ^ (1 << b);
  }
  fill(dp, dp + (1 << 26), INF);
  dp[0] = 1;
  for (int i = 0; i < C; i++) dp[1 << i] = 1;
  for (int i = 1; i < N + 1; i++) {
    for (int j = 0; j < C; j++) {
      int bit = 1 << j;
      dp[a[i]] = min(dp[a[i]], dp[a[i] ^ bit] + 1);
    }
  }
  cout << dp[a[N]] << endl;
  return 0;
}
