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)]
    seen=[False for i in range(K+M)]
    for i in range(K):
        if A[i]>=X:
            dist[i]=i
    for i in range(K+M):
        idx=-1
        mn=INF+1
        for j in range(K+M):
            if mn>dist[j] and (not seen[j]):
                idx=j
                mn=dist[j]
        seen[idx]=True
        for j in b:
            if idx<K:
                if idx+j>=K:
                    dist[K+(idx+j)%M]=min(dist[K+(idx+j)%M],dist[idx]+j)
            else:
                dist[K+(idx-K+j)%M]=min(dist[K+(idx-K+j)%M],dist[idx]+j)
    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)