#include<bits/stdc++.h>
using namespace std;
const int maxn=100010;
int n,m;
int a[maxn];
int main()
{
scanf("%d%d",&n,&m);
for(int i=1;i<=n;++i)
scanf("%d",&a[i]);
int single=min(n,m*2-n);
int pair=n-single;
int ans=a[n];
for(int h=1,t=pair;h<t;++h,--t)
ans=max(ans,a[h]+a[t]);
printf("%d\n",ans);
return 0;
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