#############################################################

import sys
sys.setrecursionlimit(10**7)

from heapq import heappop,heappush
from collections import deque,defaultdict,Counter
from bisect import bisect_left, bisect_right
from itertools import product,combinations,permutations
from math import sin,cos
#from math import isqrt #DO NOT USE PyPy

ipt = sys.stdin.readline
iin = lambda :int(ipt())
lmin = lambda :list(map(int,ipt().split()))

#############################################################

A,B,a,b = lmin()
for x in range(10**8):
    if x%A == a and x%B == b:
        print(x)
        exit()