def gcd(x, y):
    while y:
        x, y = y, x%y
    return x

def main():
    N, M = map(int, input().split())
    X = list(map(int, input().split()))
    Y = list(map(int, input().split()))

    for i in range(N*M//gcd(N, M)):
        if X[i%N] == Y[i%M]:
            return i+1
    return "-1"

if __name__ == "__main__":
    main()