#include <bits/stdc++.h>
using namespace std;
template <class T>
void read(T &first) {
  char ch;
  for (ch = getchar(); (ch < '0' || ch > '9') && ch != '-';) ch = getchar();
  first = 0;
  int t = 1;
  if (ch == '-') {
    ch = getchar();
    t = -1;
  }
  for (; ch >= '0' && ch <= '9'; ch = getchar()) first = first * 10 + ch - '0';
  first *= t;
}
char a[200010];
int b[1 << 26];
int main() {
  scanf("%s", a + 1);
  int n = strlen(a + 1);
  int m = (1 << 26);
  for (int i = 1; i < m; i++) b[i] = n;
  b[0] = 0;
  int t = 0;
  for (int i = 1; i <= n; i++) {
    t ^= (1 << (a[i] - 97));
    for (int j = 0; j < 26; j++) b[t] = min(b[t], b[t ^ (1 << j)] + 1);
  }
  printf("%d\n", b[t]);
  return 0;
}
