import heapq
INF=10**18+1
def check(X):
    b=[]
    for i in range(K-1,-1,-1):
        if B[i]>=X:
            b+=[K-i]
    if len(b)==0:
        return N<K and A[N]>=X
    M=b[0]
    dist=[INF for i in range(K+M)]
    Q=[]
    for i in range(K):
        if A[i]>=X:
            dist[i]=i
            heapq.heappush(Q,(i,i))
    while Q:
        c,v=heapq.heappop(Q)
        if dist[v]<c:
            continue
        for j in b:
            if v<K:
                if v+j>=K and dist[K+(v+j)%M]>c+j:
                    dist[K+(v+j)%M]=c+j
                    heapq.heappush(Q,(c+j,K+(v+j)%M))
            else:
                if dist[K+(v-K+j)%M]>c+j:
                    dist[K+(v-K+j)%M]=c+j
                    heapq.heappush(Q,(c+j,K+(v-K+j)%M))
    if N<K:
        return dist[N]<=N
    else:
        return dist[K+N%M]<=N
K,N=map(int,input().split())
A=list(map(int,input().split()))
B=list(map(int,input().split()))
ok=-INF
ng=INF
while ng-ok>1:
    mid=(ok+ng)//2
    if check(mid):
        ok=mid
    else:
        ng=mid
print(ok)