#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;


int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */ 
    int n,k;
    cin>>n>>k;
    int a[n],i,s[n][2],j=1,t=0,u,z,sum=0;
    for(i=0;i<n;i++)
        cin>>a[i];
    if(2*k+1<n)
        {
        for(i=0;i<2*k;i++)
            if(t>=a[i])
            {
            t=a[i];
            u=i;
        }
            s[0][0]=t;
        s[0][1]=u;
        z=u;
        while(z+2*k<=n)
            {
            t=0;
    for(i=z+k+1;i<=z+2*k;i++)
        {
       if(t>=a[i])
            {
            t=a[i];
            u=i;
        }
    }
             s[j][0]=t;
        s[j][1]=u;
            j++;
           z=u;
            
        }
        for(i=0;i<j;i++)
            sum+=s[i][0];
        cout<<sum;
    }
    else
        {
        
        sum=a[k];
       
        cout<<sum;
    }
    return 0;
}