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

def is_ok(k):
    x = max(0, (a-k)//n)
    if a-n*x >= k and b+x >= k:
        return True
    y = max(0, (b-k)//m)
    if a+y >= k and b-m*y >= k:
        return True
    return False


ok = 0
ng = 10**18+1
while ok+1 < ng:
    c = (ok+ng)//2
    if is_ok(c):
        ok = c
    else:
        ng = c
print(ok)