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

if b > a:
    a,b = b,a
    n,m = m,n


l = 0
r = (a-b+n-1)//n
def calc(x):
    nb = b + x//n
    na = a - x//n * n
    return min(na,nb)

while r > l + 2:
    c1 = (2*l+r)//3
    c2 = (l+2*r)//3
    cal1 = calc(c1*n)
    cal2 = calc(c2*n)

    if cal1 < cal2:
        l = c1
    else:
        r = c2

ans = 0
for i in range(l-1,r+2):
    ans = max(ans,calc(i*n))
print(ans)