N, K = [ int(a) for a in input().split(' ') ]
alist = [ int(a) for a in input().split(' ') ]

result = 0
taken = set()
for i in range(1,N//K+1):
    if K*i >= N:
        break
    minind, minval = min(enumerate(alist[K*i:]), key=lambda p: p[1] if p[0] in taken else float("inf"))
    result += minval
    taken.add(minind)

print(result)