a,b,n,m=map(int,input().split())
while True:

    if a==b:
        print(a)
        break

    if a > b:
        a -= n
        if a < b:
            print(b)
            break
        b += 1
    
    if a < b:
        b -= m
        if a > b:
            print(a)
            break
        a += 1