b0,c0=list(map(int,input().split()))
b1,c1=list(map(int,input().split()))
for i in range(b0*b1+1):
    if (i-c0)%b0==0 and (i-c1)%b1==0:
        print (i)
        break
    if i==b0*b1:
        print("NaN")