import sys
def input():
    return sys.stdin.readline()[:-1]
import heapq
n,k=map(int,input().split())
a=list(map(int,input().split()))
f=list(map(int,input().split()))
a.sort()
f.sort()
ans=[]
for i in range(n):
    ans.append([f[i]*a[n-i-1]*-1,a[n-i-1]*-1])
heapq.heapify(ans)
# print(ans)
for i in range(k):
    tmp=heapq.heappop(ans)
    # print(tmp)
    if tmp[1]==0:
        heapq.heappush(ans,tmp)
        break
    tmp[0]=tmp[0]//tmp[1]
    tmp[1]+=1
    tmp[0]=tmp[0]*tmp[1]
    heapq.heappush(ans,tmp)
cnt=0
for i in range(n):
    cnt=max(cnt,ans[i][0]*-1)
print(cnt)