import sys
readline=sys.stdin.readline
write=sys.stdout.write

N,M=map(int,readline().split())
A=list(map(int,readline().split()))
B=list(map(int,readline().split()))
for nm in range(N*M):
    if A[nm%N]==B[nm%M]:
        ans=nm+1
        break
else:
    ans=-1
print(ans)