#include<cstdio>
#include<cstring>
#include<algorithm>
#include<map>
using namespace std;
map<int,int> s;
char w[310001];
int i,j,k,n,f[310001],a[310001];
int main(){
	scanf("%s",w+1);n=strlen(w+1);s.clear();
	for (i=1,a[0]=f[0]=0;i<=n;i++) a[i]=a[i-1]^(1<<(w[i]-'a'));
	s[0]=0;
	for (i=1;i<=n;i++){
		f[i]=n+1;
		if (s.count(a[i])) f[i]=s[a[i]]+1;
		for (j=0;j<26;j++)
		 if (s.count(a[i]^(1<<j))) f[i]=min(f[i],s[a[i]^(1<<j)]+1);
		if (!s.count(a[i])) s[a[i]]=f[i];else s[a[i]]=min(s[a[i]],f[i]);
	}
	printf("%d\n",f[n]);
	return 0;
}