#include <iostream>
#include <fstream>
#include <deque>

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

int n,k;
deque<int> dq, ddq;

void inserare(int x)
{
    while ( ! dq.empty() && dq.back() > x)
    {
        dq.pop_back();
    }
    dq.push_back(x);
}

void golire(int x)
{
    if( ! dq.empty() && dq.front() == x)
    {
        dq.pop_front();
    }
}

int main()
{
    f>>n>>k;
    int x;
    for(int i=0; i<k; ++i)
    {
        f>>x;
        ddq.push_back(x);
        inserare(x);
    }
    long long rezultat=dq.front();
    //cout << dq.front() << ' ';
    for(int i=k,x; i<n; ++i)
    {
        f>>x;
        inserare(x);
        ddq.push_back(x);

        golire(ddq.front());
        ddq.pop_front();

        rezultat += (long long)dq.front();
        //cout << dq.front() << ' ';
    }
    g<<rezultat << endl;
    return 0;
}