#include <fstream>

#define NMAX 5000020

using namespace std;

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

int n, k, x, top, bot;
long long int sum;

struct deq{
    int val, ind;
};
deq stiv[NMAX];

int main()
{
    f >> n >> k;

    for(int i = 1; i <= n; i++)
    {
        f >> x;

        while(top >= bot && stiv[top].val > x)
            top--;
        stiv[++top].val = x; stiv[top].ind = i;

        if(i >= k)
        {
             while(stiv[bot].ind <= i - k)
                bot++;

            sum += stiv[bot].val;
        }
    }

    g << sum;
    return 0;
}