// (⁠◕⁠ᴗ⁠◕⁠✿⁠)

#include <bits/stdc++.h>
#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#define rep(i, n) for (ll i = 0; i < (n); i++)
#define srep(i, s, n) for (ll i = s; i < (n); i++)
#define len(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
using namespace std;
template<typename T> using vc = vector<T>;
template<typename T> using vv = vc<vc<T>>;
template<typename T> using vvv = vv<vc<T>>;
using vi = vc<int>;using vvi = vv<int>; using vvvi = vv<vi>;
using ll = long long;using vl = vc<ll>;using vvl = vv<ll>; using vvvl = vv<vl>;
using ld = long double; using vld = vc<ld>; using vvld = vc<vld>; using vvvld = vc<vvld>;
using uint = unsigned int;
using ull = unsigned long long;
const ld pi = acos(-1.0);
const int inf = 0x3f3f3f3f;
const ll INF = 0x3f3f3f3f3f3f3f3f;
// const ll mod = 1000000007;
const ll mod = 998244353;
inline bool inside(ll y, ll x, ll H, ll W) {return 0 <= (y) and (y) < (H) and 0 <= (x) and (x) < (W); }

#define debug(var)  do{std::cout << #var << " : \n";view(var);}while(0)
template<typename T> void view(T e){cout << e << endl;}
template<typename T> void view(const vc<T>& v){for(const auto& e : v){ cout << e << " "; } cout << endl;}
template<typename T> void view(const vv<T>& vv){ for(const auto& v : vv){ view(v); } }

vc<pair<ll, ll>> factorization(ll &N){
    vc<pair<ll, ll>> factors;
    ll tmp = N;
    for (ll i = 2; i * i <= N + 1; i++){
        if (tmp % i == 0){
            int cnt = 0;
            while (tmp % i == 0){
                tmp /= i;
                cnt += 1;
            }
            factors.push_back({i, cnt});
        }
    }
    if (tmp != 1){
        factors.push_back({tmp, 1});
    }
    if (len(factors) == 0){
        factors.push_back({N, 1});
    }
    return factors;
}

void solve(){
    ll A, B;cin >> A >> B; 
    ll C = B - A;
    if (C == 0){
        cout << 0 << endl;
        return;
    }
    auto factor = factorization(C);
    ll ans = INF;
    function<void(int, ll)> dfs = [&](int p, ll nw){
        if (len(factor) == p) return;
        auto [prime, num] = factor[p];
        dfs(p + 1, nw);
        if (nw >= A) ans = min(ans, nw - A);
        rep(i, num){
            nw *= prime;
            if (nw >= A){
                ans = min(ans, nw - A);
                break;
            }
            dfs(p + 1, nw);
        }
    };
    dfs(0, 1);
    if (ans == INF) cout << -1 << endl;
    else cout << ans << endl;
}

int main(){
    int T; cin >> T;
    while (T--) solve();
}