#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");

int main(void)
{
    long long N,K,i,j, cnt_deque=0, rez=0;
    long long *v = nullptr, *deque = nullptr;
    fin>>N>>K;
    v = new long long[N];
    deque = new long long[N];
    for(i=0;i<N;i++)
    {
        fin >> v[i];
    }
    for(i=0;i<N;i++)
    {
        deque[cnt_deque] = i;
        while (cnt_deque >0 && v[deque[cnt_deque]] < v[deque[cnt_deque-1]])
        {
            deque[cnt_deque-1] = i;
            cnt_deque--;
        }
        cnt_deque ++;
        if(i>= K -1)
        {
            if(deque[0] <= i - K)
            {
                for(j=1;j<cnt_deque;j++)
                {
                    deque[j-1] = deque[j];
                }
                cnt_deque--;
            }
            rez = rez + v[deque[0]];
        }
    }
    fout << rez;
    delete[]v;
    delete[]deque;
    return 0;
}