#include <iostream>
#include <cstdio>
#include <deque>
#define NMAX 5000005
using namespace std;

int N,K,v[NMAX];
long long S;
deque<int> q;
void citire()
{
    scanf("%d%d",&N,&K);
    for(int i=1;i<=N;i++)
        scanf("%d",&v[i]);
}

void adauga(int i)
{
    while(!q.empty()&&v[q.back()]>v[i])
        q.pop_back();
    q.push_back(i);
}

void init()
{
    for(int i=1;i<=K;i++)
        adauga(i);
    S+=v[q.front()];
}

void primul(int i)
{
    if(!q.empty()&&i-q.front()+1>K)
        q.pop_front();
}

void rezolvare()
{
    for(int i=K+1;i<=N;i++)
    {
        adauga(i);
        primul(i);
        S+=v[q.front()];
    }
}

void afisare()
{
    printf("%lld\n",S);
}

int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    citire();
    init();
    rezolvare();
    afisare();

    return 0;
}