#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using mint = modint998244353;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vvvll = vector<vvll>;
using vmi = vector<mint>;
using vvmi = vector<vmi>;
using vvvmi = vector<vvmi>;
#define all(a) (a).begin(), (a).end()
#define rep2(i, m, n) for (int i = (m); i < (n); ++i)
#define rep(i, n) rep2(i, 0, n)
#define drep2(i, m, n) for (int i = (m)-1; i >= (n); --i)
#define drep(i, n) drep2(i, n, 0)

void solve(){
    ll a, b; cin >> a >> b;
    if(b%a == 0){
        cout << 0 << endl;
        return;
    }
    if(b-2*a<0){
        cout << -1 << endl;
        return;
    }
    if(a == 1){
        cout << 0 << endl;
        return;
    }
    vi dv;
    int c = b-a;
    for(int i = 1; i*i <= c; i++){
        if(c%i == 0){
            dv.push_back(i);
            if(c/i != i)dv.push_back(c/i);
        }
    }sort(all(dv));
    int i = 0;
    while(c/dv[i] >= a)i++;
    i--;
    cout << c/dv[i] - a << endl;
}

int main(){
    int t; cin >> t;
    while(t--)solve();

    return 0;
}