#include <bits/stdc++.h>
#include <bits/extc++.h>
using i64 = long long;
namespace internal
{
    template <typename T>
    T safe_mod(T x, T m)
    {
        x %= m;
        if (x < 0)
            x += m;
        return x;
    }

    template <typename T>
    T pow_mod(T x, T n, T m)
    {
        assert(0 <= n && 1 <= m);
        if (m == 1)
            return 0;
        T r = 1, y = safe_mod(x, m);
        while (n)
        {
            if (n & 1)
                r = (r % y) % m;
            y = (y * y) % m;
            n >>= 1;
        }
        return r;
    }

    template <typename T>
    std::pair<T, T> inv_gcd(T a, T b)
    {
        a = safe_mod(a, b);
        if (a == 0)
            return {b, 0};
        T s = b, t = a;
        T m0 = 0, m1 = 1;
        while (t)
        {
            T u = s / t;
            s -= t * u;
            m0 -= m1 * u;
            auto tmp = s;
            s = t;
            t = tmp;
            tmp = m0;
            m0 = m1;
            m1 = tmp;
        }
        if (m0 < 0)
            m0 += b / s;
        return {s, m0};
    }

    template <typename T>
    T inv_mod(T x, T m)
    {
        assert(1 <= m);
        auto z = inv_gcd(x, m);
        assert(z.first == 1);
        return z.second;
    }

    //(rem,mod)
    template <typename T>
    std::pair<T, T> crt(const std::vector<T> &r, const std::vector<T> &m)
    {
        assert(r.size() == m.size());
        int n = (int)r.size();
        T r0 = 0, m0 = 1;
        for (int i = 0; i < n; i++)
        {
            assert(1 <= m[i]);
            T r1 = safe_mod(r[i], m[i]), m1 = m[i];
            if (m0 < m1)
            {
                std::swap(r0, r1);
                std::swap(m0, m1);
            }
            if (m0 % m1 == 0)
            {
                if ((r0 % m1) != r1)
                    return {0, 0};
                continue;
            }
            T g, im;
            std::tie(g, im) = inv_gcd(m0, m1);
            T u1 = m1 / g;
            if ((r1 - r0) % g)
                return {0, 0};
            long long x = (r1 - r0) / g % u1 * im % u1;
            r0 += x * m0;
            m0 *= u1;
            if (r0 < 0)
                r0 += m0;
        }
        return {r0, m0};
    }
}

void solve()
{
    int A, B, a, b;
    std::cin >> A >> B >> a >> b;
    auto crt = internal::crt<int>({a, b}, {A, B});
    std::cout << crt.first << '\n';
}
int main()
{
    std::cin.tie(nullptr)->sync_with_stdio(false);
    solve();
    return 0;
}