#include<cstdio>
#include<cstring>
const int N=2e5+7;
char a[N];
int sum[N];
int f[N];
int g[(1<<26)];
inline int min(int a,int b)
{
	return a<b?a:b;
}
int main()
{
	scanf("%s",a+1);
	int len=strlen(a+1);
	for(int i=1;i<=len;i++)	sum[i]=sum[i-1]^(1<< (a[i]-'a') );
	memset(f,127,sizeof(f));
	memset(g,127,sizeof(g));
	g[0]=0;
	for(int i=1;i<=len;i++)
	{
		f[i]=min(f[i],g[sum[i]]+1);
		for(int j=0;j<=25;j++)	
		f[i]=min(f[i],g[sum[i]^(1<<j)]+1);
		g[sum[i]]=min(g[sum[i]],f[i]);
	}
	printf("%d\n",f[len]);
	return 0;
}