a,b,n,m=map(int,input().split())
ok=0
ng=10**20
while abs(ok-ng)>1:
    num=(ok+ng)//2
    if num<=a:
        a1=num
        b1=b+(a-num)//n
    else:
        if num<=b:
            b1=num
            a1=a+(b-num)//m
        else:
            b1=0
            a1=0
    if min(b1,a1)>=num:
        ok=num
    else:
        ng=num
print(ok)