"""
多重平衡二分木
挿入、削除、bisect、k番目の値の取得,k番目までの値の和の取得がO(logL)で可能
同じ値には違うidを与えて区別する
idが足りなくなったらid数を二倍にして保持している値を一から挿入しなおすことでならし計算量がO(logL+logK)になるはず…
あらかじめid数を設定することもできる

verify:ABC127F,ABC170E
"""
class MultiBalancingTree:
    def __init__(self, n,id=0):
        self.N = n
        self.id_size=id
        self.root = self.node(1<<(n+self.id_size), 1<<(n+self.id_size),self.id_size)
        self.val_dic={}

    def debug(self):
        def debug_info(nd_):
            return (nd_.value,(nd_.value - 1)>>self.id_size, nd_.pivot , nd_.left.value - 1 if nd_.left else -1, nd_.right.value - 1 if nd_.right else -1,nd_.cnt)

        def debug_node(nd):
            re = []
            if nd.left:
                re += debug_node(nd.left)
            if nd.value: re.append(debug_info(nd))
            if nd.right:
                re += debug_node(nd.right)
            return re
        print("Debug - root =", self.root.value - 1, debug_node(self.root)[:50])

    def rebuild(self,v):
        self.id_size+=1
        #print("rebuild:",self.id_size)
        self.root=self.node(1<<(self.N+self.id_size), 1<<(self.N+self.id_size),self.id_size)
        check=[]
        for val in self.val_dic:
            cnt=self.val_dic[val]
            self.val_dic[val]=0
            for j in range(cnt):
                self.append(val)
        self.append(v)

    def append(self,v):
        if v not in self.val_dic:
            self.val_dic[v]=0
        id=self.val_dic[v]
        if id>=2**self.id_size:
            self.rebuild(v)
        else:
            V=(v<<self.id_size)+id
            self.val_dic[v]+=1
            self._append(V)

    def _append(self, v):
        v += 1
        nd = self.root
        while True:
            if v == nd.value:
                return 0
            else:
                nd.cnt+=1
                nd.sum+=(v-1)>>self.id_size
                mi, ma = min(v, nd.value), max(v, nd.value)
                if mi < nd.pivot:
                    nd.value = ma
                    if nd.left:
                        nd = nd.left
                        v = mi
                    else:
                        p = nd.pivot
                        nd.left = self.node(mi, p - (p&-p)//2,self.id_size)
                        break
                else:
                    nd.value = mi
                    if nd.right:
                        nd = nd.right
                        v = ma
                    else:
                        p = nd.pivot
                        nd.right = self.node(ma, p + (p&-p)//2,self.id_size)
                        break

    def kth(self,k):
        cnt=k
        nd=self.root
        while True:
            if nd.left:
                if nd.left.cnt<k:
                    k-=nd.left.cnt+1
                    if nd.right:
                        nd=nd.right
                    else:
                        raise IndexError("BalancingTree doesn't hold kth number")
                elif nd.left.cnt==k:
                    return (nd.value-1)>>self.id_size
                else:
                    nd=nd.left
            else:
                if k==0:
                    return (nd.value-1)>>self.id_size
                if nd.right:
                    k-=1
                    nd=nd.right
                else:
                    raise IndexError("BalancingTree doesn't hold kth number")

    def kth_sum(self,k):
        if k==-1:
            return 0
        cnt=k
        res_sum=0
        nd=self.root
        while True:
            if nd.left:
                if nd.left.cnt<k:
                    k-=nd.left.cnt+1
                    res_sum+=nd.left.sum+((nd.value-1)>>self.id_size)
                    if nd.right:
                        nd=nd.right
                    else:
                        raise IndexError("BalancingTree doesn't hold kth number")
                elif nd.left.cnt==k:
                    res_sum+=nd.left.sum+((nd.value-1)>>self.id_size)
                    return res_sum,(nd.value-1)>>self.id_size
                else:
                    nd=nd.left
            else:
                if k==0:
                    return res_sum+((nd.value-1)>>self.id_size),(nd.value-1)>>self.id_size
                if nd.right:
                    k-=1
                    res_sum+=((nd.value-1)>>self.id_size)
                    nd=nd.right
                else:
                    raise IndexError("BalancingTree doesn't hold kth number")

    def kth_sum_big(self,k):
        res_sum=self.sum
        if self.size>k:
            res_sum-=self.kth_sum(self.size-k-2)
            return res_sum
        else:
            raise IndexError("BalancingTree doesn't hold kth number")

    def leftmost(self, nd):
        while nd.left:
            nd=nd.left
        return nd

    def rightmost(self, nd):
        while nd.right:
            nd=nd.right
        return nd

    def find_l(self, v):
        v += 1
        nd = self.root
        prev = 0
        if nd.value < v: prev = nd.value
        while True:
            if v <= nd.value:
                if nd.left:
                    nd = nd.left
                else:
                    return (prev - 1)>>self.id_size
            else:
                prev = nd.value
                if nd.right:
                    nd = nd.right
                else:
                    return (prev - 1)>>self.id_size

    def find_r(self, v):
        v += 1
        nd = self.root
        prev = 0
        if nd.value > v: prev = nd.value
        while True:
            if v < nd.value:
                prev = nd.value
                if nd.left:
                    nd = nd.left
                else:
                    return (prev - 1)>>self.id_size
            else:
                if nd.right:
                    nd = nd.right
                else:
                    return (prev - 1)>>self.id_size

    @property
    def max(self):
        if self.size:
            return self.find_l((1<<(self.N+self.id_size))-1)
        return 0

    @property
    def min(self):
        if self.size:
            return self.find_r(-1)
        return 0

    @property
    def sum(self):
        return self.root.sum-((self.root.value-1)>>self.id_size)

    @property
    def size(self):
        return self.root.cnt-1

    def delete(self,v):
        id=self.val_dic[v]-1
        if id==-1:
            raise IndexError("You are an idiot")
        V=(v<<self.id_size)+id
        self._delete(V)
        self.val_dic[v]-=1

    def _delete(self, v, nd = None, prev = None):
        v += 1
        if not nd: nd = self.root
        if not prev: prev = nd
        while v != nd.value:
            prev = nd
            nd.cnt-=1
            nd.sum-=(v-1)>>self.id_size
            if v <= nd.value:
                if nd.left:
                    nd = nd.left
                else:
                    return
            else:
                if nd.right:
                    nd = nd.right
                else:
                    return
        nd.cnt-=1
        nd.sum-=(v-1)>>self.id_size
        if (not nd.left) and (not nd.right):
            if not prev.left:
                prev.right=None
            elif not prev.right:
                prev.left=None
            else:
                if nd.pivot==prev.left.pivot:
                    prev.left=None
                else:
                    prev.right=None
        elif nd.right:
            nd.value = self.leftmost(nd.right).value
            self._delete(nd.value - 1, nd.right, nd)
        else:
            nd.value = self.rightmost(nd.left).value
            self._delete(nd.value - 1, nd.left, nd)

    def __contains__(self, v: int) -> bool:
        return self.find_r(v - 1) == v

    def __len__(self):
        return self.size

    class node:
        def __init__(self, v, p, m):
            self.value = v
            self.pivot = p
            self.left = None
            self.right = None
            self.cnt=1
            self.sum=(v-1)>>m

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

ans = 10**18
BT = MultiBalancingTree(30,id=18)
for i in range(1,N+1):
    if i*K>N:
        break
    tmp = A[i*K-1]
    for j in range((i-1)*K,i*K-1):
        BT.append(A[j])
    if i>=2:
        tmp += BT.kth_sum(i-2)[0]
    ans = min(ans,tmp)

print(ans)