#include<iostream>
#include<string>
#include<queue>
#include<vector>
#include<cassert>
#include<random>
#include<set>
#include<map>
#include<cassert>
#include<unordered_map>
#include<bitset>
#include<numeric>
#include<algorithm>
using namespace std;
typedef long long ll;
const int inf=1<<30;
const ll INF=1LL<<62;
typedef pair<int,ll> P;
typedef pair<int,P> PP; 
const ll MOD=998244353;


ll solve(){
    ll A,B;
    cin>>A>>B;
    ll d=B-A;
    if(d==0){
        return 0;
    }
    ll C=INF;
    for(ll m=1;m*m<=d;m++){
        if(d%m==0){
            if(m>=A){
                C=min(C,m);
            }
            if(d/m>=A){
                C=min(C,d/m);
            }
        }
    }
    if(C==INF){
        return -1;
    }
    return C-A;
}

int main(){
    int T;
    cin>>T;
    vector<ll> ans(T);
    for(int t=0;t<T;t++){
        ans[t]=solve();
    }

    for(int t=0;t<T;t++){
        cout<<ans[t]<<endl;
    }
}