#include<cstdio>
#include<cstring>
#define mem(a,p) memset(a,p,sizeof(a))
const int N=2e5+10,M=1<<26;
char ch[N];
int f[N],len,g[M];
int ss[N];
int min(int x,int y){return x>y?y:x;}
int main(){
	mem(g,127);
	scanf("%s",ch+1);
	len=strlen(ch+1);
	for(int i=1;i<=len;i++)ss[i]=ss[i-1]^(1<<(ch[i]-'a'));
	g[0]=0;
	for(int i=1;i<=len;i++){
		f[i]=g[ss[i]]+1;
		for(int j=0;j<=25;j++)
			f[i]=min(f[i],g[ss[i]^(1<<j)]+1);
		g[ss[i]]=min(f[i],g[ss[i]]);
	}
	printf("%d",f[len]);
	return 0;
}