from math import *

def lcm(x, y):
    return x*y//gcd(x, y)

B0, C0 = map(int, input().split())
B1, C1 = map(int, input().split())
C0 %= B0
C1 %= B1

for i in range(lcm(B0, B1)):
    if i%B0==C0 and i%B1==C1:
        print(i)
        break
else:
    print('NaN')