include<iostream>

using namespace std; int main() { int t,n,k,i; cin>>t; while(t--) { cin>>n>>k;

    if(n==1)
    {
    if(k==1)
    cout<<"1"<<endl;
    else
    cout<<"-1"<<endl;
    }
    else
    {

    if(k>n/2)
    cout<<"-1"<<endl;
    else {

    for(i=1;i<=k;i++)
    {
        cout<<(i<<1);



    }cout<<endl;
    }
    }



}
return 0;

}