#include <iostream>
using namespace std;
using ll = long long;
const int inf = 2e9;

// B + X = k(A + X)
// B - A = (k - 1)(A + X)
int A, B;
void solve(){
    cin >> A >> B;
    if(A == B){
        cout << 0 << "\n";
        return;
    }
    int N = B - A;
    int ans = inf;
    for(int i = 1;i * i <= N;i++){
        if(N % i != 0)continue;
        if(i >= A){
            ans = min(ans, i - A);
        }
        if(N / i >= A){
            ans = min(ans, N / i - A);
        }
    }
    cout << (ans == inf ? -1 : ans) << "\n";
}
int main(void){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    
    int t; cin >> t;
    while(t--)solve();
    return 0;
}