from heapq import heappush, heappop

H = []
hpush = lambda x: heappush(H, x)
hpop = lambda: heappop(H)
hmin = lambda: H[0] if H else 0

N, K = map(int, input().split())
A = [int(a) for a in input().split()]
s = 0
for i in range(N - K + 1, N):
    a = A[i]
    s += a
    hpush(a)

ans = 0
for i in range(N - K + 1)[::-1]:
    a = A[i]
    if i % 2:
        ans = max(ans, s + a)
    
    m = hmin()
    if K > 1 and a > m:
        hpush(a)
        hpop()
        s += a - m
    
print(ans)