import sys
input = sys.stdin.readline

N,M=map(int,input().split())
A=list(map(int,input().split()))
B=list(map(int,input().split()))

for i in range(N*M):
    if A[i%N]==B[i%M]:
        print(i+1)
        break
    _ = 0
else:
    print(-1)