#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

const int maxn = 2e5, inf = 1e9;

int n;
char s[maxn + 1];
int a[maxn + 1];
int f[maxn + 1], minf[1 << 26];

int main(void) {
  scanf("%s", s);
  n = strlen(s);
  for (int i = 0; i < n; ++i) {
    a[i + 1] = a[i] ^ (1 << (s[i] - 'a'));
  }
  fill(minf, minf + (1 << 26), inf);
  f[0] = 0;
  minf[0] = 0;
  for (int i = 1; i <= n; ++i) {
    f[i] = minf[a[i]];
    for (int j = 0; j < 26; ++j) {
      f[i] = min(f[i], minf[a[i] ^ (1 << j)]);
    }
    ++f[i];
    minf[a[i]] = min(minf[a[i]], f[i]);
  }
  printf("%d\n", f[n]);
  return 0;
}
