#include <bits/stdc++.h>
using namespace std;

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int T; cin >> T;
    while(T--){
        long long a,b; cin >> a >> b;
        if(a == b){cout << 0 << endl; continue;}
        long long diff = b-a;

        vector<long long> D;
        for(int i=1; i*i<=diff; i++){
            if(diff%i) continue;
            D.push_back(i);
            D.push_back(diff/i);
        }
        sort(D.begin(),D.end());
        int answer = -1;
        for(auto d : D) if(d >= a){answer = d-a; break;}
        cout << answer << endl;
    }
}