#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
char c;
int now,f[67109000];
int main() {
	c=getchar();
	for (int i=1;i<67109000;i++)
	f[i]=1000000;
	f[0]=0; now=0;
	while (c>='a'&&c<='z') {
		int w=c-'a';
		now=now^(1<<w);
		//f[now]++;
		for (int i=0;i<26;i++)
		f[now]=min(f[now],f[now^(1<<i)]+1);
		//printf("%d %d\n",now,f[now]);
		c=getchar();
	}
	printf("%d\n",max(f[now],1));
	return 0;
}