from atcoder.math import crt


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


def solve(A, B, a, b):
    ans, _ = crt([a, b], [A, B])

    return ans


def main():
    A, B, a, b = map(int, input().split())
    ans = solve(A, B, a, b)
    print(ans)


if __name__ == "__main__":
    main()