from heapq import heappush,heappop,heapify

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

if K==1:
    exit(print(A[0]))

ans = 10**18
que = []
S = 0
for i in range(1,N+1):
    if i*K>N:
        break
    tmp = A[i*K-1]
    if i!=1:
        t = A[(i-1)*K:i*K-1]
        t.sort(reverse=True)
        while t and -que[0] > t[-1]:
            S += que[0]
            heappop(que)
            S += t[-1]
            heappush(que,-t.pop())
    tmp += S
    ans = min(ans,tmp)
    S += A[i*K-1]
    heappush(que,-A[i*K-1])

print(ans)