#include<iostream>
#include<cassert>
using namespace std;
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int T;cin>>T;
	for(;T--;)
	{
		int A,B;
		cin>>A>>B;
		if(B%A==0)
		{
			cout<<"0\n";
			continue;
		}
		int ansX=B+1;
		for(int k=2;(k-1)*(k-1)<=B;k++)
		{
			int t=B-k*A;
			if(t>=0&&t%(k-1)==0)
			{
				int X=t/(k-1);
				ansX=min(ansX,X);
			}
		}
		for(int X=0;X*X<=B;X++)
		{
			if((B+X)%(A+X)==0)ansX=min(ansX,X);
		}
		if(ansX==B+1)cout<<"-1\n";
		else cout<<ansX<<"\n";
	}
}