def extended_gcd(a, b):
    if a == 0:
        return b, 0, 1
    else:
        g, x, y = extended_gcd(b % a, a)
        return g, y - (b // a) * x, x

def modinv(a, m):
    g, x, y = extended_gcd(a, m)
    if g != 1:
        raise Exception('逆元が存在しません')
    else:
        return x % m

def find_minimum_x(A, B, a, b):
    M = A * B
    M1 = M // A
    M2 = M // B

    M1_inv = modinv(M1, A)
    M2_inv = modinv(M2, B)

    x = (a * M2 * M2_inv + b * M1 * M1_inv) % M

    return x

# 入力を取得
A, B, a, b = map(int, input().split())

# 結果を出力
result = find_minimum_x(A, B, a, b)
print(result)