#include <iostream>
#include <string>
#include <vector>
#include <cmath>
using namespace std;
int main()
{
	int t;
	cin>>t;
	for(int k=1;k<=t;++k)
	{
		string s;
		cin>>s;
		if(s.size()%2!=0)
		{
			cout<<-1<<endl;
			continue;
		}
		string s1,s2;
		for(int i=0;i<s.size()/2;++i)
			s1.push_back(s[i]);
		for(int i=s.size()/2;i<s.size();++i)
			s2.push_back(s[i]);
		vector<int> a(27,0),b(27,0);
		for(int i=0;i<s1.size();++i)
			++a[s1[i]-'a'];
		for(int j=0;j<s2.size();++j)
			++b[s2[j]-'a'];
		int ans=0;
		for(int i=0;i<a.size();++i)
			ans+=abs(a[i]-b[i]);
		cout<<ans/2<<endl;
	}
}