import sys, itertools
 
sys.setrecursionlimit(500005)
stdin = sys.stdin

ni = lambda: int(ns())
na = lambda: list(map(int, stdin.readline().split()))
ns = lambda: stdin.readline().strip()

a, b, n, m = na()

ans = 0

def con(a, b, n):
    if (a - b) % n == 0:
        return (a - b) // n - 1
    
    else:
        return (a - b) // n

if a < b:
    c = con(b, a, m)
    a += c
    b -= m * (c + 1)
        
elif a > b:
    c = con(a, b, n)
    a -= n * (c + 1)
    b += c

print(max(a, b))