#include <fstream>

using namespace std;

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

int a;
int b;
int vec[9000009];
int deque[9000009];

int main()
{
    fin >> a >> b;

    for (int i=1;i<=a;i++)
        fin >> vec[i];

    int front=1;
    int back=0;
    long long s=0;

    for (int i=1;i<=a;i++)
    {
        while (front<=back && vec[i]<=vec[deque[back]])
            back--;

        back++;
        deque[back]=i;

        if (deque[front]==i-b) front++;

        if (i>=b) s+=vec[deque[front]];
    }
    fout << s;
}