#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <cstring>
using namespace std;
int n,k;
int cost[100000];
int dp[10000][10000];
int dp1[10000];


long long int rec(int start)
    {
    long long int mina = 10000000000;
        
    if(n-1 <= start+k)
        {
        int ans = cost[start];
        for(int i=start+1;i<n;i++)
            {
            if(ans > cost[i])
                ans = cost[i];
        }
        return ans;
    }
    else if(dp1[start]!=-1)
        return dp1[start];
    else
        {
        mina = cost[start] + rec(start + k + 1);
        for(int i=start+1;i<=start+k;i++)
        {
            if(!(mina <= cost[i]))
            mina = min(mina,cost[i] + rec(i+k+1));
        }
        
    }
    return mina;
}

long long int recurr(int start,int end)
    {
    if(start>end)
        return 0;
    else if(end <= start + k)
        {
        long long int ans= cost[start];
        for(int i=start + 1;i<=end;i++)
        {
                if(ans > cost[i])
                    ans = cost[i];
        }   
        return ans;
     }
        
        
    else if(dp[start][end] != -1)
            return dp[start][end];
    
    long long int mina = 100000;
    for(int i=start;i<=start+k;i++)
        {
        for(int j=end-k;j<=end;j++)
            {
            if(i!=j)
                {
                if(!(cost[i]+cost[j] > mina))
                      mina = min(mina,cost[i]+cost[j]+recurr(i+k+1,j-k-1));
              }
            else
                return cost[i];
            
        }
    }
    return mina;
}

int main() {
    memset(dp1,-1,sizeof(dp1));
    cin>>n>>k;
    for(int i=0;i<n;i++)
        {
        cin>>cost[i];
    }
    cout<<rec(0)<<endl;
    return 0;
}