#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");

int deq[5000001], a[5000001], st=1, dr, i, n, k;
long long sum;

int main()
{
    f>>n>>k;
    for (i=1; i<=n; i++)
        f>>a[i];
    for (i=1; i<=n; i++)
    {
        while (st<=dr && a[i] <= a[deq[dr]])
            dr--;
        dr++;
        deq[dr] = i;
        if(deq[st] == i-k)
            st++;
        if (i>=k)
            sum += a[deq[st]];
    }
    g<<sum;
    return 0;
}