int main() {
    int t;
    cin>>t;
    while(t--){
        string s;
        cin>>s;
        int n = s.size();
        if(n%2!=0)
            cout<<-1<<endl;
        else{
            int sum = 0;
            int arr1[26] = {0};
            for(int i=0;i<(n/2);i++){
                arr1[s[i]-'a']++;
                }
            for(int i=(n/2);i<n;i++){
                arr1[s[i]-'a']--;
                }
            for(int i=0;i<26;i++){
                if(arr1[i]>0)
                    sum = sum+arr1[i];
            }
            cout<<sum<<endl;}
       }
return 0;
}