CB---Calvin's Game

n,k=map(int,input().split())
arr=[0]
arr.extend(list(map(int,input().split())))

dpb=[0 for i in range(n+1)]
dpf=[0 for i in range(n+1)]
dpb[1]=arr[1]
dpb[2]=arr[2]+arr[1]
for i in range(k+1,n+1):
    dpf[i]=arr[i]+max(dpf[i-1],dpf[i-2])
for i in range(1,n+1):
    dpb[i]=arr[i]+max(dpb[i-1],dpb[i-2])
ans=0
for i in range(1,n+1):
    ans=max(ans,dpf[i]+dpb[i]-arr[i])
print(ans)