#include <bits/stdc++.h>

using namespace std;

ifstream fin ("deque.in");
ofstream fout ("deque.out");

int main()
{
    int v1[500001],nr,dis,start;
    int s=0;
    fin>>nr>>dis;
    start=1;
    for(int i=start;i<=nr;i+=1)
    {
        int x;
        fin>>x;
        v1[i]=x;
    }


    while(start<= nr-dis+1)
    {
        int minim = v1[start];
        for(int i=start ; i<= start+dis-1 ; i+=1)
        {
            if(v1[i] < minim )
                minim = v1[i];
        }
        s=s+minim;
        start++;




    }

    fout<<s;




    return  0;
}