import collections

class MaxQueue(collections.deque):
    def enqueue(self, val):
        count = 1
        while self and self[-1][0] < val:
            count += self.pop()[1]
        self.append([val, count])

    def dequeue(self):
        ans = self.max()
        self[0][1] -= 1
        if self[0][1] <= 0:
            self.popleft()
        return ans

    def max(self):
        return self[0][0] if self else 0

readlist = lambda: list(map(int, input().split()))
N, K = readlist()
A = readlist()
P = [0]
for x in A:
    P.append(P[-1] + x)
for x in A:
    P.append(P[-1])

dp = [0] * (N + K + 1)
maxq = MaxQueue()
length = 0
for i in range(N - 1, -1, -1):
    maxq.enqueue(dp[i+2] + P[i+1])
    if i <= N-K:
        maxq.dequeue()
    dp[i] = max(dp[i+1], maxq.max() - P[i])

print(dp[0])