#include <bits/stdc++.h>
//#include <atcoder/modint>
using namespace std;
//using namespace atcoder;
//using mint = modint998244353;
#define rep(i,n) for(long long i=0;i<n;i++)
#define rep1(i,n) for(long long i=1;i<=n;i++)
#define Rep(i,a,b) for(long long i=a;i<=b;i++)
#define all(a) (a).begin(), (a).end()
#define fst first
#define snd second
typedef unsigned long long ull;
typedef long long ll;
typedef vector<int> vec;
typedef vector<vector<int>> vvec;
typedef vector<long long> vecll;
typedef vector<vector<long long>> vvecll;

//#include<boost/multiprecision/cpp_int.hpp>
//using namespace boost::multiprecision;

const ll mod=998244353;

class mint {
public:
    long long x;
    constexpr mint(long long x=0) : x((x%mod+mod)%mod) {}
    constexpr mint operator-() const { 
      return mint(-x);
    }
    constexpr mint& operator+=(const mint& a) {
        if ((x += a.x) >= mod) x -= mod;
        return *this;
    }
    constexpr mint& operator-=(const mint& a) {
        if ((x += mod-a.x) >= mod) x -= mod;
        return *this;
    }
    constexpr mint& operator*=(const mint& a) {
        (x *= a.x) %= mod;
        return *this;
    }
    constexpr mint operator+(const mint& a) const {
        mint res(*this);
        return res+=a;
    }
    constexpr mint operator-(const mint& a) const {
        mint res(*this);
        return res-=a;
    }
    constexpr mint operator*(const mint& a) const {
        mint res(*this);
        return res*=a;
    }
    constexpr mint pow(long long t) const {
        if (!t) return 1;
        mint a = pow(t>>1);
        a *= a;
        if (t&1) a *= *this;
        return a;
    }

    // for prime mod
    constexpr mint inv() const {
        return pow(mod-2);
    }
    constexpr mint& operator/=(const mint& a) {
        return (*this) *= a.inv();
    }
    constexpr mint operator/(const mint& a) const {
        mint res(*this);
        return res/=a;
    }
};
ostream& operator<<(ostream& os, const mint& m){
    os << m.x;
    return os;
}


//xのn乗をpで割ったあまりを求める
ll modpow(ll x,ll n,ll p=mod){
  if(n==0) return 1;
  if(n%2==1) return (x*modpow(x,n-1,p))%p;
  else{
    ll t=modpow(x,n/2,p);
    assert(t>0);
    return (t*t)%p;
  }
}

//xの逆元(p:素数)
ll inv(ll x,ll p=mod){
  return modpow(x,p-2,p);
}

template <typename T>
int index(vector<T> &a, T x){
	return lower_bound(all(a),x)-a.begin();
}

const ll mod2=1000000009;

const ll INF=5e18;
const int INT_INF=1e9;
const double pi=3.14159265358979;


int main(){
	int t;
  cin >> t;
  rep(i,t){
    ll a,b;
    cin >> a >>b;
    ll c=b-a;
    vector<ll> fact;
    if(c==0){
      cout << 0 << endl;
      continue;
    }
    for(ll i=1;i*i<=c;i++){
      if(i*i==c){
        fact.push_back(i);
      }else if(c%i==0){
        fact.push_back(i);
        fact.push_back(c/i);
      }
    }
    sort(all(fact));
    ll ans=-1;
    for(ll x:fact){
      if(a<=x){
        ans=x-a;
        break;
      }
    }
    cout << ans << endl;
  }
	return 0;
}