"""
部分列の個数 -> M

M = 1:
    自明
M = 2:
    1個目 [K, 2K - 1]
    2個目 [2K, N]
M = 3:
    1個目 [K, 3K - 2]
    2個目 [2K, N]
    3個目 [3K, N]
M = M:
    1個目 [K, M(K - 1) + 1]
    x個目 [xK, N]

[xk, N] の部分を流用して全探索？

"""
class SegTree:
    def __init__(self, n, e, ope, lst=[]):
        self.N0 = 2 ** (n - 1).bit_length()
        self.e = e
        self.ope = ope
        self.data = [e] * (2 * self.N0)
        if lst:
            for i in range(n):
                self.data[self.N0 + i] = lst[i]
            for i in range(self.N0 - 1, 0, -1):
                self.data[i] = self.ope(self.data[2 * i], self.data[2 * i + 1])
    
    def build(self):
        for i in range(self.N0 - 1, 0, -1):
            self.data[i] = self.ope(self.data[2 * i], self.data[2 * i + 1])
                
    def update(self, i, x): #a_iの値をxに更新
        i += self.N0
        self.data[i] = x
        while i > 1:
            i >>= 1
            self.data[i] = self.ope(self.data[2 * i], self.data[2 * i + 1])
    
    def add(self, i, x):
        self.update(i, x + self.get(i))

    def set(self, i, x):
        self.data[self.N0 + i] = x
    
    def query(self, l, r): #区間[l, r)での演算結果
        if r <= l:
            return self.e
        lres = self.e
        rres = self.e
        l += self.N0
        r += self.N0
        while l < r:
            if l & 1:
                lres = self.ope(lres, self.data[l])
                l += 1
            if r & 1:
                r -= 1
                rres = self.ope(self.data[r], rres)
            l >>= 1
            r >>= 1
        return self.ope(lres, rres)
    
    def get(self, i): #a_iの値を返す
        return self.data[self.N0 + i]

import heapq
from heapq import *

class Heapq:
    def __init__(self, lst = [], reverse = False):
        if reverse:
            self.pm = -1
            self.hq = [-l for l in lst]
        else:
            self.pm = 1
            self.hq = lst.copy()
        heapq.heapify(self.hq)
        self.tot = sum(lst)
        self.cnt = {}
        self.length = len(lst)
    
    def __bool__(self):
        return self.length > 0
        
    def __len__(self):
        return self.length
    
    def __getitem__(self, i):
        if i == 0:
            return self.top()
        else:
            assert False
    
    def push(self, x):
        self.length += 1
        self.cnt[x * self.pm] = self.cnt.get(x * self.pm, 0) + 1
        heapq.heappush(self.hq, x * self.pm)
        self.tot += x
    
    def pop(self):
        if self.length == 0:
            return None
        self.length -= 1
        ret = heapq.heappop(self.hq)
        self.tot -= self.pm * ret
        self.cnt[ret] -= 1
        self.delete()
        return self.pm * ret
    
    def top(self):
        if self.hq:
            return self.pm * self.hq[0]
        else:
            return None
    
    def remove(self, x):
        if self.cnt.get(x * self.pm, 0) == 0:
            return False
        self.cnt[x * self.pm] -= 1
        self.length -= 1
        self.tot -= x
        self.delete()
        return True
            
    def delete(self):
        while self.hq and self.cnt.get(self.hq[0], 0) == 0:
            heapq.heappop(self.hq)

n, k = map(int, input().split())
A = list(map(int, input().split()))
if k == 1:
    print(A[0])
    exit()

inf = 1 << 30
def ope(x, y):
    if x[0] <= y[0]:
        return x
    else:
        return y

e = (inf, -1)
seg = SegTree(n, e, ope, [(a, i) for i, a in enumerate(A)])

ans = A[k - 1]
ind = Heapq()
hq = []
x = n // k
tot = 0
for i in range(x, 1, -1):
    a, i = seg.query(i * k - 1, n)
    ind.push(i)
    tot += a
    seg.update(i, e)
    hq.append((-a, i))
heapify(hq)

for i in range(x, 1, -1):
    mind = ind.top()
    if mind <= i * (k - 1):
        a = seg.query(k - 1, n)[0]
        ans = min(ans, tot + a)
    else:
        a = seg.query(k - 1, i * (k - 1) + 1)[0]
        ans = min(ans, tot + a)
    a, i = heappop(hq)
    tot += a
    seg.update(i, (-a, i))
    ind.remove(i)
print(ans)