#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000001
#define Inf64 1000000000000000001


int main(){
	int _t;
	cin>>_t;
	rep(_,_t){
		long long a,b;
		cin>>a>>b;
		if(a==b){
			cout<<0<<endl;
			continue;
		}
		long long d = b-a;
		vector<long long> y;
		for(long long i=1;i*i<=d;i++){
			if(d%i==0)y.push_back(i),y.push_back(d/i);
		}
		long long ans = Inf64;
		rep(i,y.size()){
			if(y[i] < a)continue;
			ans = min(ans,y[i]-a);
		}
		if(ans==Inf64)ans = -1;
		cout<<ans<<endl;
	}
	
	return 0;
}