a,b,c,d = map(int,input().split())

if a > b:
    e = (a - b) // (c + 1)
    a -= c * e
    b += e
    r = min(a,b)
    while a > b:
        a -= c
        b += 1
        r = max(r,min(a,b))

else:
    e = (b - a) // (d + 1)
    b -= d * e
    a += e
    r = min(a,b)
    while b > a:
        b -= d
        a += 1
        r = max(r,min(a,b))
print(r)