#include <iostream>
#include <stdio.h>
#include <cstdlib>
using namespace std;

struct lista
{
    int info;
    int position;
    lista *left;
    lista *right;
}*start,*end;

int pozmin;

void pop_left()
{
    lista *cpy = start;
    if (start -> right != NULL)
    {
        start-> right -> left = NULL;
        start = start -> right;
    }
    else
    {
        start = NULL;
    }

    if (start == NULL)
    {
        end = NULL;
    }
    delete(cpy);


}

void pop_right()
{
    lista *cpy = end;

    if (end -> left != NULL)
    {
        end -> left -> right = NULL;
        end = end -> left;
    }
    else
    {
        end = NULL;
    }

    if (end == NULL)
    {
        start = NULL;
    }
    delete(cpy);
}
void push_right(int x,int poz)
{

    lista *p = new lista();
    p -> info = x;
    p -> right = NULL;
    p -> position = poz;
    if (end != NULL)
    {
        end -> right = p;
        p -> left = end;
        end = p;
    }
    else
    {
        end = new lista();
        end = p;
    }

    if (start == NULL)
    {
        start = p;
    }

    pozmin = start -> position;
}

int main()
{

    FILE *input = fopen("deque.in","r");
    FILE *output = fopen("deque.out","w");
    int n,k;
    long long sum = 0;
    fscanf(input,"%d",&n);
    fscanf(input,"%d",&k);
    int x;
    for (int i=0;i<k;i++)
    {

        fscanf(input,"%d",&x);

        while (end != NULL)
        {
            if (end -> info >= x) pop_right();
            else break;

        }
        push_right(x,i);


    }

    pozmin = start -> position;
    sum += start -> info;
    for (int i=k;i<n;i++)
    {

        fscanf(input,"%d",&x);
        if (pozmin + k - 1< i)
        {
            pop_left();
            pozmin = start -> position;
        }


        while (end != NULL)
        {
            if (end -> info >= x) pop_right();
            else break;

        }
        push_right(x,i);
        sum += start -> info;

    }
    fprintf(output,"%lld",sum);
    fclose(input);
    fclose(output);
    return 0;
}