#include <stdio.h>
#include <vector>
#include <algorithm>
#include <queue>

std::priority_queue<int, std::vector<int>, std::greater<int> > Q;

int x[200010];
int main()
{
	int a,b;
	scanf("%d%d",&a,&b);
	for(int i=1;i<=a;i++) scanf("%d",&x[i]);
	
	if(b==1)
	{
		int max = x[2];
		for(int i=2;i<=a;i+=2) max = max>x[i]?max:x[i];
		printf("%d",max);
		return 0;
	}
	
	long long int ans = 0, sum = 0;
	for(int i=a;i>=1;i--)
	{
		if(i%2==0 && Q.size()==b-1)
		{
			long long int val = sum + x[i];
			ans = ans>val?ans:val;
		}
		
		if(Q.size()<b-1)
		{
			Q.push(x[i]);
			sum += x[i];
		}
		else
		{
			if(Q.top()<x[i])
			{
				sum -= Q.top();
				sum += x[i];
				Q.pop();
				Q.push(x[i]);
			}
		}
	}
	printf("%lld",ans);
}