"""

"""

import sys
from sys import stdin

A,B,N,M = map(int,input().split())

l = 0
r = 10**19

while r-l != 1:

    m = (l+r)//2

    nA = A-m
    nB = B-m

    if nA < 0 and nB < 0:
        r = m
    elif nA < 0:
        nA += nB // M

        if nA >= 0:
            l = m
        else:
            r = m
    
    elif nB < 0:
        nB += nA // N
        if nB >= 0:
            l = m
        else:
            r = m
    else:
        l = m

print (l)