#include <fstream>
#define NMAX 50000020

using namespace std;

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

int v[NMAX], Deq[NMAX], n, k, i, st = 1, dr;
long long s;

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

    for(i = 1; i <= n; ++ i)
    {
        f >> v[i];

        while(st <= dr && v[i] <= v[ Deq[dr] ])
            dr --;

        Deq[++ dr] = i;

        while(Deq[st] <= i - k)
            st ++;

        if(i >= k)
          s = s + v[ Deq[st] ];
    }

    g << s;

    f.close();
    g.close();

    return 0;
}