import sys
input = sys.stdin.readline

from heapq import heappop,heappush

N,K=map(int,input().split())
A=list(map(int,input().split()))


S=[(0,-1)]

for i in range(N-1,-1,-1):
    S.append((S[-1][0]+A[i],i))

score=0
SX=[]

for i in range(len(S)):
    if S[i][1]==0:
        score+=S[i][0]
    elif S[i][1]>=1:
        SX.append(S[i])

SX.sort()

Q=[]
while len(Q)<K-1:
    x,y=SX.pop()

    heappush(Q,(-y,x))
    score+=x

ANS=score

for i in range(N-1,K-1,-1):
    # iを削除

    score-=A[i]*K

    while Q and -Q[0][0]>=i:
        heappop(Q)

        x,y=SX.pop()
        heappush(Q,(-y,x))
        score+=x

    ANS=max(ANS,score)

print(ANS)