#include <bits/stdc++.h>
using namespace std;
int minn[67108865], f[200001], a[200001];
char c[200001];
const int inf = 1e8;
int main() {
  scanf("%s", c + 1);
  int n = strlen(c + 1);
  for (register int i = 1; i <= n; i++) a[i] = a[i - 1] ^ (1 << (c[i] - 'a'));
  int all = (1 << 26) - 1;
  for (register int i = 1; i <= all; i++) minn[i] = inf;
  for (register int i = 1; i <= n; i++) {
    f[i] = minn[a[i]] + 1;
    f[i] = min(f[i], f[i - 1] + 1);
    for (register int j = 0; j < 26; j++)
      if (a[i] & (1 << j)) f[i] = min(f[i], minn[a[i] ^ (1 << j)] + 1);
    minn[a[i]] = min(minn[a[i]], f[i]);
  }
  cout << f[n] << endl;
  return 0;
}
