import math
A,B,N,M = map(int, input().split())
if A < B:
    num = math.ceil(B/M)
    A += num
    for i in range(num):
        B = B - M
    if A > B:
        A -= 1
        B = B + M
    print(A)
if A > B:
    num = math.ceil(A/N)
    B += num
    for i in range(num):
        A = A - N
    if A < B:
        B -= 1
        A = A + N
    print(B)