#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
//const int INF = 1e9;
const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n) - 1; i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r) - 1;i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
//約数列挙
std::vector<long long> divisorEnumeration(long long n) {
	std::vector<long long> x;
	for (long long i = 1; i*i <= n; i++) {
		if (0 == n % i) {
			x.push_back(i);
			if (n != i * i) x.push_back(n / i);
		}
	}
	std::sort(x.begin(), x.end());
	return x;
}
int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int t; cin >> t;
	while (t--) {
		int a, b; cin >> a >> b;
		int d = b - a;
		if (0 == d) {
			cout << 0 << endl;
			continue;
		}
		long long  ans = LINF;
		auto v = divisorEnumeration(d);
		rep(i, v.size()) {
			int na = v[i];
			int p = d / v[i];
			if (na < a)continue;
			chmin(ans, na - a);
		}
		if (LINF == ans)ans = -1;
		cout << ans << endl;
	}
	return 0;
}