#include <bits/stdc++.h>
using namespace std;

map<long,long>mp;
long getAns(long arr[],long index,long max1,long k)
    {
        if(index>=max1)
               return 0;
        if(mp[index]!=0)
            return mp[index];
        long minPos1=-1,min1=LONG_MAX,minPos2=-1,min2=LONG_MAX,i;
        for(i=index;i>=max(0L,index-k);--i)
            {
                if(arr[i]<min1)
                    {
                        min1=arr[i];
                        minPos1=i;
                    }
            }
        for(i=index;i<=min(max1-1,index+k);++i)
            {
                if(arr[i]<min2)
                    {
                        min2=arr[i];
                        minPos2=i;
                    }
            }
        mp[index]=min(arr[minPos1]+getAns(arr,minPos1+k+1,max1,k),arr[minPos2]+getAns(arr,minPos2+k+1,max1,k));
        return mp[index];
    }
struct node
    {
        long cost;
        long range;
        long init;
    };
bool compare(const node &a,const node &b)
    {
        if(a.cost==b.cost)
            {
                if(a.range==b.range)
                    return a.init>b.init;
                return a.range>b.range;
            }
        return a.cost<b.cost;
    }

int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
    long i,j,k,cost,n,N,K;
    cin>>N>>K;
    long arr[N+5];
    vector<node> arr1(N);
    for(i=0;i<N;++i)
        {
            scanf("%ld",&arr[i]);
            arr1[i].init=max(0L,i-K);
            arr1[i].range=min(N-1,i+K)-max(0L,i-K)+1;
            arr1[i].cost=arr[i];
        }
    sort(arr1.begin(),arr1.end(),compare);
    vector<int> visited(N,0);
    cost=0;
    for(i=0;i<N;++i)
        {
           // int flag=0;
            //cout<<arr1[i].init<<" "<<arr1[i].range<<endl;
            for(j=arr1[i].init;j<=arr1[i].init+arr1[i].range-1;++j)
                if(!visited[j]) break;
            if(j!=(arr1[i].init+arr1[i].range))
                {
                    cost+=arr1[i].cost;
                    for(j=arr1[i].init;j<=arr1[i].init+arr1[i].range-1;++j) visited[j]=1;
                }
        }
    cout<<cost<<endl;
    //cout<<getAns(arr,0,N-1,K)<<endl;
    
    return 0;
}