from heapq import*
n,k,*A = map(int,open(0).read().split())
Q = []
S = [0]*(n+1)
for i in range(n)[::-1]:
  S[i] = S[i+1]+A[i]
M = S[:]
for i in range(n)[::-1]:
  M[i] = min(M[i],M[i+1])
ans = -1<<60
Q = []
sm = S[0]
if k==1:
  ans = sm-M[1]
else:
  for i in range(1,n):
    heappush(Q,S[i])
    sm += S[i]
    if len(Q)==k-1:
      ans = max(ans,sm-M[i+1]*k)
      sm -= heappop(Q)
print(ans)