import heapq
class Heap():
    def __init__(self, maxi = False):
        self.sum = 0
        self.al = []
        self.maxi = maxi
        self.len = 0

    def __len__(self):
        return len(self.al)

    def add(self, x):
        if self.maxi:
            heapq.heappush(self.al, -x)
        else:
            heapq.heappush(self.al, x)
        self.sum += x
    
    def pop(self):
        if self.maxi:
            now = heapq.heappop(self.al)
            self.sum += now
            return -now
        else:
            now = heapq.heappop(self.al)
            self.sum -= now
            return now

    def top(self):
        now = self.pop()
        self.add(now)
        return now
def solve(n, k, a):
    Q = Heap()
    ans = 0
    for i in range(n - 1, -1, -1):
        if i % 2 == 1:
            ans = max(ans, a[i] + Q.sum)
        Q.add(a[i])
        if len(Q) >= k:
            Q.pop()
    return ans

n, k = map(int,input().split())

a = list(map(int,input().split()))

print(solve(n, k , a))