from collections import defaultdict

A,B,a,b=map(int,input().split())

d=defaultdict(int)
for i in range(a, 3000, A ):
 d[i] += 1
for i in range(b, 3000, B ): d[i] += 1

ans=999999
for k in d: ans=min(ans, k if d[k] ==2 else 999999)

print(ans)