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

#define For(i, a, b) for(int i = (a); i < (b); i++)
#define rep(i, n) For(i, 0, n)
#define rFor(i, a, b) for(int i = (a); i >= (b); i--)
#define ALL(v) (v).begin(), (v).end()
#define rALL(v) (v).rbegin(), (v).rend()

using lint = long long;
using ld = long double;

int INF = 2000000000;
lint LINF = 1000000000000000000;

struct SetupIo {
    SetupIo() {
        ios::sync_with_stdio(false);
        cin.tie(nullptr);
        cout << fixed << setprecision(15);
    }
} setupio;

template <class T>
T bin_gcd(T a_, T b_) {
    unsigned long long a = abs(a_), b = abs(b_);
    if (a == 0 || b == 0) {
        return (a == 0 ? b : a);
    }
    int x = __builtin_ctzll(a), y = __builtin_ctzll(b);
    a >>= x;
    b >>= y;
    while (a != b) {
        if (a < b) {
            swap(a, b);
        }
        a -= b;
        a >>= __builtin_ctzll(a);
    }
    return (a << min(x, y));
}

// ax + by = gcd(a, b) を満たす (x, y) を求める
// c が gcd(a, b) で割り切れないと、ax + by = c を満たす c は存在しない
// 負の数の場合の処理に注意
long long extGCD(long long a, long long b, long long &x, long long &y) {
    if (b == 0) {
        x = 1;
        y = 0;
        return a;
    }
    long long d = extGCD(b, a % b, y, x);
    y -= a / b * x;
    return d;
}

template <class T>
T div_floor(T a, T b) {
    assert(b != 0);
    if (b < 0) {
        a = -a;
        b = -b;
    }
    return (a >= 0 ? a / b : (a + 1) / b - 1);
}

template <class T>
T div_ceil(T a, T b) {
    assert(b != 0);
    if (b < 0) {
        a = -a;
        b = -b;
    }
    return (a > 0 ? (a - 1) / b + 1 : a / b);
}

const lint mod = 1000000000;

int main() {
    int TT;
    cin >> TT;
    while (TT--) {
        lint n, m;
        cin >> n >> m;
        lint g = bin_gcd(mod, n);
        if (m % g != 0) {
            cout << -1 << "\n";
            continue;
        }
        lint x, y;
        extGCD(mod, -n, x, y);
        if (mod * x - n * y == -g) {
            x = -x;
            y = -y;
        }
        x *= (m / g);
        y *= (m / g);
        lint add = mod / g;
        lint p = div_ceil<lint>(-y, add);
        y += p * add;
        cout << y << "\n";
    }
}