#include <iostream>
#include <vector>
#include <cmath>
#include <numeric>
#include <algorithm>
#include <set>
#include <unordered_set>
#include <cstring>
#include <unordered_map>
#include <iomanip>
#include <queue>
#include <map>
#include <sstream>
#include <stack>
#include <bitset>
#include <random>

using ll = long long;

using namespace std;

void solve() {
    int x, y;
    cin >> x >> y;
    for (int i = 1; i <= 100; ++i) {
        if (i % x && i % y) {
            cout << i << "\n";
            return;
        }
    }
    cout << "-1\n";
}

int main() {
    #ifdef LOCAL
    freopen("input.txt", "r", stdin);
    // freopen("output.txt", "w", stdout);
    #endif
    ios::sync_with_stdio(0);
    cin.tie(0);
    int t;
    cin >> t;
    while (t--) solve();
}