#include <bits/stdc++.h>
using namespace std;
const double eps = 1e-8;
const double PI = acos(-1.0);
template <class T>
int chkmin(T &a, T b) {
  return a > b ? a = b, 1 : 0;
}
template <class T>
int chkmax(T &a, T b) {
  return a < b ? a = b, 1 : 0;
}
template <class T>
T sqr(T a) {
  return a * a;
}
template <class T>
T mmin(T a, T b) {
  return a < b ? a : b;
}
template <class T>
T mmax(T a, T b) {
  return a > b ? a : b;
}
template <class T>
T aabs(T a) {
  return a < 0 ? -a : a;
}
char s[102000];
int a[102000], f[102000], smn[70000000];
void js(int x) {
  int s = a[x];
  f[x] = smn[s] + 1;
  for (int i = 0; i < 26; ++i) chkmin(f[x], smn[s ^ (1 << i)] + 1);
  chkmin(smn[s], f[x]);
}
int main() {
  int n;
  scanf("%s", s + 1);
  n = strlen(s + 1);
  for (int i = 1, t = 1 << 26; i < t; ++i) smn[i] = 0x3f3f3f3f;
  for (int i = 1; i <= n; ++i) {
    a[i] = a[i - 1] ^ (1 << (s[i] - 'a'));
    js(i);
  }
  printf("%d\n", f[n]);
  return 0;
}
