import sys
#input = sys.stdin.readline
#input = sys.stdin.buffer.readline #文字列はダメ
#sys.setrecursionlimit(1000000)
#import math
import bisect
#import itertools
#import random
#from heapq import heapify, heappop, heappush
from collections import defaultdict
#from collections import deque
import copy #DeepCopy: hoge = [_[:] for _ in hogehoge]
#from functools import lru_cache
#@lru_cache(maxsize=None)
#MOD = pow(10,9) + 7
MOD = 998244353
#dx = [1,0,-1,0]
#dy = [0,1,0,-1]
#dx8 = [1,1,0,-1,-1,-1,0,1]
#dy8 = [0,1,1,1,0,-1,-1,-1]

def main():
    b0,c0 = map(int,input().split())
    b1,c1 = map(int,input().split())

    for x in range(10000000):
        if (x-c0)%b0 == 0 and (x-c1)%b1 == 0:
            exit(print(x))
    print('NaN')



if __name__ == '__main__':
    main()