A,B,N,M = map(int, input().split())
while 1:
    if A < B:
        B = B - M
        A += 1
        if A > B:
            B = B + M
            A -= 1
            break
    elif A > B:
        A = A - N
        B += 1
        if A < B:
            A = A + N
            B -= 1
            break
print(min(A, B))