n,m = map(int,input().split())
a = list(map(int,input().split()))
b = list(map(int,input().split()))
len_a,len_b = len(a),len(b)
import math
ans = -1
LMC = len_a * len_b // math.gcd(len_a,len_b)
for i in range(LMC):
#     print(a[i % len_a],b[i % len_b],i+1)
    if a[i % len_a] == b[i % len_b]:
        ans = i+1
        break
print(ans)