#include <bits/stdc++.h>
using namespace std;
double EPS = 1e-9;
int INF = 1000000005;
long long INFF = 1000000000000000005LL;
double PI = acos(-1);
int dirx[8] = {-1, 0, 0, 1, -1, -1, 1, 1};
int diry[8] = {0, 1, -1, 0, -1, 1, -1, 1};
inline string IntToString(long long a) {
  char x[100];
  sprintf(x, "%lld", a);
  string s = x;
  return s;
}
inline long long StringToInt(string a) {
  char x[100];
  long long res;
  strcpy(x, a.c_str());
  sscanf(x, "%lld", &res);
  return res;
}
inline string GetString(void) {
  char x[1000005];
  scanf("%s", x);
  string s = x;
  return s;
}
inline string uppercase(string s) {
  int n = (int)s.size();
  for (int(i) = (0); (i) < (n); ++(i))
    if (s[i] >= 'a' && s[i] <= 'z') s[i] = s[i] - 'a' + 'A';
  return s;
}
inline string lowercase(string s) {
  int n = (int)s.size();
  for (int(i) = (0); (i) < (n); ++(i))
    if (s[i] >= 'A' && s[i] <= 'Z') s[i] = s[i] - 'A' + 'a';
  return s;
}
inline void OPEN(string s) {
  freopen((s + ".in").c_str(), "r", stdin);
  freopen((s + ".out").c_str(), "w", stdout);
}
map<int, int> kanan;
string s;
int dp[200005];
int pre[200005];
int main() {
  s = GetString();
  int st = 0;
  kanan[st] = -1;
  for (int(i) = (0); (i) < ((int)s.size()); ++(i)) {
    pre[i] = st;
    st ^= (1 << (s[i] - 'a'));
    kanan[st] = i;
  }
  dp[(int)s.size()] = 0;
  for (int(i) = ((int)s.size() - 1); (i) >= (0); --(i)) {
    int &ret = dp[i];
    ret = INF;
    if (kanan.count(pre[i]) && kanan[pre[i]] >= i)
      ret = min(ret, dp[kanan[pre[i]] + 1] + 1);
    for (int(j) = (0); (j) < (26); ++(j)) {
      int nxt = pre[i] ^ (1 << j);
      if (kanan.count(nxt) && kanan[nxt] >= i)
        ret = min(ret, dp[kanan[nxt] + 1] + 1);
    }
  }
  printf("%d\n", dp[0]);
  return 0;
}
