n, k = map(int, input().split())
arr = list(map(int, input().split()))

# Sort the array by value, keeping track of their 1-based indices
sorted_arr = sorted([(a, i+1) for i, a in enumerate(arr)], key=lambda x: x[0])

m = n // k
sum_ans = 0
ptr = len(sorted_arr) - 1  # Starting from the end of the sorted array

for i in range(1, m + 1):
    required_pos = n - (i * k) + 1
    while ptr >= 0:
        if sorted_arr[ptr][1] >= required_pos:
            sum_ans += sorted_arr[ptr][0]
            ptr -= 1
            break
        else:
            ptr -= 1

print(sum_ans)