#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;
int min_we(int a[],int m,int n){
    int smallest=a[m];
    for (int i = m; i < n; i++) {
    if (a[i] < smallest) {
        smallest = a[i];
        }
    }
    return smallest;
}

int main() {
    int n,k,count=0;
    cin>>n>>k;
    int a[10000];
    for(int i=0;i<n;i++){
        cin>>a[i];
    }
    if(k>n)
        cout<<min_we(a,0,n)<<endl;
    else{
        for(int i=0;i<n-2*k;i++){
            count+=min_we(a,i,i+2*k);
        }
        cout<<count<<endl;
    
    }    
    return 0;
}