#include <cstdio>
#include <iostream>
#include <string>
using namespace std;
#define ref(i,x,y)for(int i=x;i<=y;++i)
string s;
int n,ans,a[1<<26];
int main()
{
	cin>>s;
	n=s.size();
	s=" "+s;
	int t=0;
	a[0]=1;
	ans=2e9;
	ref(i,1,n)
	{
		t=t^(1<<(s[i]-'a'));
		int tmp=2e9;
		if(a[t])tmp=a[t];
		ref(j,0,25)
		{
			int tt=t^(1<<j);
			if(a[tt])tmp=min(tmp,a[tt]);
		}
		if(i==n)ans=tmp+1;
		if(!a[t])a[t]=tmp+1;
		else a[t]=min(a[t],tmp+1);
	}
	cout<<ans-1<<endl;
}