#include<bits/stdc++.h>
#define rep(i,n) for(int i=0;i<n;i++)
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<long long> vl;
typedef vector<vector<int>> vvi;
typedef vector<vector<long long>> vvl;
typedef pair<int,int> P;
typedef long double ld;

template<typename T>istream& operator>>(istream& is, vector<T>& v){int n = v.size(); assert(n > 0); rep(i, n) is >> v[i]; return is;}
template<typename U, typename T> ostream& operator<<(ostream& os, const pair<U, T>& p){os << p.first << ' ' << p.second; return os;}
template<typename T>ostream& operator<<(ostream& os, const vector<T>& v){int n = v.size(); rep(i, n) os << v[i] << (i == n - 1 ? "\n" : " "); return os;}
template <typename T>ostream& operator<<(ostream& os, const vector<vector<T>>& v){int n = v.size(); rep(i, n) os << v[i] << (i == n - 1 ? "\n" : ""); return os;}

template<typename T> void chmin(T& a, T b){a = min(a, b);}
template<typename T> void chmax(T& a, T b){a = max(a, b);}

const int INF = 1001001001;

int solve(){
	int a, b;
	cin >> a >> b;
	if(b % a == 0){
		cout << "0\n";
		return 0;
	}
	int d = b - a;
	set<int> se;
	for(int x = 1; x * x <= d; x++){
		if(d % x == 0){
			se.insert(x);
			se.insert(d / x);
		}
	}
	int ans = INF;
	for(int x : se){
		int c = d / x;
		if(c < a) continue;
		chmin(ans, c - a);
	}
	if(ans == INF) cout << "-1\n";
	else cout << ans << "\n";
	return 0;
}

int main(){
	int t;
	cin >> t;
	rep(_, t) solve();
	return 0;
}