def solve_one():
    A, B, a, b = map(int, input().split())
    for x in range(0, 10**9):
        if x % A == a and x % B == b:
            print(x)
            return
            

if __name__ == "__main__":
    T = 1#int(input())
    for i in range(1, T + 1):
        solve_one()