#include <bits/stdc++.h>
using namespace std;
const int maxn = 200000 + 50;
char a[maxn];
int f[maxn], sum[1 << 27];
int main() {
  scanf("%s", a + 1);
  int n = strlen(a + 1);
  memset(sum, 0x3f, sizeof(sum));
  int g = 0;
  f[0] = 0;
  sum[0] = 0;
  for (int i = 1; i <= n; ++i) {
    int x = 1 << (a[i] - 'a');
    g ^= x;
    f[i] = sum[g];
    for (int j = 0; j < 26; ++j) f[i] = min(sum[g ^ (1 << j)], f[i]);
    ++f[i];
    sum[g] = min(sum[g], f[i]);
  }
  cout << f[n] << endl;
  return 0;
}
