a,b = map(int,input().split())
c,d = map(int,input().split())
s = b % a
t = d % c
check = 0
for i in range(1000):
  for j in range(1000):
    if s + a*i == t + c*j:
      print(s+a*i)
      check = 1
      exit()
    if s + a*i < t + c*j:
      break
print('NaN')