#include<bits/stdc++.h>
using namespace std;
char s[200005];
int mp[67110000];
int hsh[200005];
int main(){
	scanf("%s",s+1);
	int n=strlen(s+1);
	for (int i=1;i<=n;i++)
		hsh[i]=hsh[i-1]^(1<<(s[i]-'a'));
	memset(mp,120,sizeof(mp));
	mp[0]=0;
	for (int i=1;i<=n;i++){
		int tmp=1e9;
		for (int j=0;j<26;j++)
			tmp=min(tmp,mp[hsh[i]^(1<<j)]+1);
		if (i==n) printf("%d",min(tmp,mp[hsh[i]]+1));
		else mp[hsh[i]]=min(mp[hsh[i]],tmp);
	}
}