#include<bits/stdc++.h>
using namespace std;
int n,a,b;
int main(){
    cin>>n;
    for(int i=1;i<=n;i++){
        cin>>a>>b;
        if((a-2)/2+1<b){
            cout<<-1<<endl;
            continue;
        }
        for(int j=1;j<=a-(2*b+1);j++) cout<<0; 
        for(int j=1;j<=b;j++) cout<<10;
        cout<<1<<endl;
    }
    return 0;
}

求助！！！！！