#include<bits/stdc++.h>
using namespace std;
int f[70000000],a[1000000],sum,l;
char s[1000000];
int main(){
	ios::sync_with_stdio(false);
	cin>>s;l=strlen(s);for (int i=1;i<=l;i++)a[i]=a[i-1]^(1<<(s[i-1]-'a'));
	memset(f,10,sizeof(f));f[0]=0;
	for (int i=1;i<=l;i++){
		sum=f[a[i]]+1;for (int j=0;j<26;j++)sum=min(sum,f[a[i]^(1<<j)]+1);
		f[a[i]]=min(f[a[i]],sum);
	}cout<<sum<<endl;
}
/*
aabcddee
*/