#include <bits/stdc++.h>
using namespace std;
const int inf = 1e9;
const int N = 2e5 + 10;
int f[N];
int ma[1 << 26];
int main() {
  string s;
  cin >> s;
  int n = s.length();
  fill(ma + 1, ma + (1 << 26), inf);
  ma[0] = 0;
  for (int i = 1, mask = 0; i <= n; i++) {
    mask ^= 1 << (s[i - 1] - 'a');
    f[i] = ma[mask];
    for (int j = 0; j < 26; j++) {
      int cmask = mask ^ (1 << j);
      f[i] = min(f[i], ma[cmask] + 1);
    }
    ma[mask] = f[i];
  }
  cout << f[n];
}
