import sys

# sys.setrecursionlimit(200005)
int1 = lambda x: int(x)-1
pDB = lambda *x: print(*x, end="\n", file=sys.stderr)
p2D = lambda x: print(*x, sep="\n", end="\n\n", file=sys.stderr)
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()

# dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
inf = (1 << 63)-1
# inf = (1 << 31)-1
# md = 10**9+7
md = 998244353

from collections import deque

n, k = LI()
aa = LI()
cs = [0]
for a in aa: cs.append(cs[-1]+a)

dp = [0]+[-inf]*n
mx = deque()
mx.append((0, 0))
mx.append((1, -cs[1]))
for i, a in enumerate(aa):
    while mx[0][0] < i+1-(k-1): mx.popleft()
    dp[i+1] = max(dp[i], cs[i+1]+mx[0][1])
    if i == n-1: break
    v = dp[i+1]-cs[i+2]
    while mx and mx[-1][-1] <= v: mx.pop()
    mx.append((i+2, v))

# pDB(dp)
print(dp[-1])