#include <iostream>
#include <queue>
#include <fstream>

using namespace std;

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

deque <int> q;
int N;
int v[5000000];

int main()
{
    fin>>N;
    int len;
    fin>>len;
    int i,k;
    int s=0;
    int a;
    int ok=0;
    for(i=0;i<N;i++)
        fin>>v[i];
    for(i=0;i<N;i++)
    {
        k=0;
        ok=0;
        if(N-i==len-1)
            break;
        while(k<len)
        {
            if(ok==0)
            {
                q.push_front(v[i+k]);
                ok=1;
            }
            if(v[i+k]<=q.front())
                q.push_front(v[i+k]);
            else
                q.push_back(v[i+k]);
            k++;
        }
        s+=q.front();
    }

    fout<<s;
    return 0;
}