#!/usr/bin/env python3
import sys


def main():
    N, M = map(int, input().split())
    A = list(map(int, input().split()))
    B = list(map(int, input().split()))
    for i in range(M * N):
        if A[i % N] == B[i % M]:
            print(i + 1)
            return
    print(-1)
    return

if __name__ == '__main__':
    main()