#堀江伸一 会津大学オンラインジャッジ問3554 Combination 合格
def f()
	return gets.split(" ").map{|e| e.to_i}
end
n,m=f()
xs=f()
ys=f()
 
s1=n-m
dp=[]
(s1+1).times{|i|
	dp<<xs[i]*ys[0]
}
if m==1 then
	puts dp.max
else
	1.upto(m-1){|p1|
		t=dp[0]
		dp.map!{|t2|
			if t<t2 then
				t=t2
			end
			t
		}
		dp2=[0]*(s1+1)
		t=0
		(s1+1).times{|p2|
			p3=p1+p2
			#p [p1,p2,p3]
			if p2==0 then
				dp2[0]=dp[0]+xs[p3]*ys[p1]
				t=dp2[0]
			else
 
				dp2[p2]=[t,dp[p2]+xs[p3]*ys[p1]].max
				t=[t,dp2[p2]].max
			end
		}
		#p dp
		dp=dp2
 
	}
	puts dp.max
end

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MTAgNAoxIDIgMyA0IDUgNiA3IDggOSAxMAozIDIgMSAwCgo=

10 4
1 2 3 4 5 6 7 8 9 10
3 2 1 0