#include <bits/stdc++.h>
using namespace std;
// #include <atcoder/modint>
// using namespace atcoder;
// using mint = modint998244353;
using ll = long long;
#define fix(x) fixed << setprecision(x)
#define rep(i, n) for(int i = 0; i < n; ++i)
#define all(x) (x).begin(),(x).end()
template<class T>bool chmin(T&a, const T&b){if(a>b){a=b;return 1;}return 0;}
template<class T>bool chmax(T&a, const T&b){if(a<b){a=b;return 1;}return 0;}
constexpr ll INFLL = (1LL << 62), MOD = 998244353;
constexpr int INF = (1 << 30);

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int t;
    cin >> t;
    while(t--){
        ll n,k;
        cin >> n >> k;
        ++k;
        for(;;++k){
            bool f = true;
            for(ll i=2;i*i<=k&&f;++i){
                if(k%i==0) f = false;
            }
            if(f) break;
        }
        ll ans = n/k*k;
        if(ans==0) ans = -1;
        cout << ans << '\n';
    }
    return 0;
}