#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N=2000000+5;
int a[N];
struct sdf{
	int val,id;
}b[N];
bool cmp(sdf x,sdf y){
	if (x.val!=y.val)return x.val<y.val;
	return x.id<y.id;
}
int main(){
	freopen("EmptyGraph.in","r",stdin);
	freopen("EmptyGraph.out","w",stdout);
	int n,k;scanf("%d%d",&n,&k);
	for (int i=1;i<=n;i++){
		scanf("%d",&a[i]);b[i]={a[i],i};
	}
	sort(b+1,b+n+1,cmp);b[n+1].id=1;
	int tmp=a[b[k].id];
	for (int i=1;i<=k;i++)a[b[i].id]=1e9;
	int mx=0,pos=a[b[k+1].id];
	for (int i=1;i<n;i++){
		mx=max(mx,min(min(a[i],a[i+1]),2*pos));
		mx=min(mx,1000000000);
	}
	if (k>=2)mx=max(mx,min(1000000000,2*tmp));
	else mx=max(mx,min(2*tmp,b[n].val));
	printf("%d\n",mx);
	return 0; 
}