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

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

print(max(a, b))