#include <bits/stdc++.h>
using namespace std;
int f[68000000];
string s;
int dp[300000];
int main() {
  cin >> s;
  long long k = 0;
  long long n = s.size();
  f[0] = 1;
  dp[0] = 0;
  for (int i = 1; i <= n; i++) {
    k ^= (1 << (s[i - 1] - 'a'));
    dp[i] = dp[i - 1] + 1;
    for (int j = 0; j < 26; j++) {
      if (f[k ^ (1 << j)]) dp[i] = min(dp[i], dp[f[k ^ (1 << j)] - 1] + 1);
    }
    if (f[k]) dp[i] = min(dp[i], dp[f[k] - 1] + 1);
    if (dp[f[k] - 1] >= dp[i]) f[k] = i + 1;
  }
  cout << dp[n];
  return 0;
}
