#include <iostream>
#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int v[5000001], n, k, stanga, dreapta, suma, deq[5000001];
int main()
{
    f>>n>>k;
    for(int i = 1; i <= n; i++)
        f>>v[i];
    stanga = 1;
    dreapta = 0;
    for(int i = 1; i <= n; i++)
    {
        while(stanga <= dreapta && v[i] <= v[deq[dreapta]])
            dreapta--;
        dreapta++;
        deq[dreapta] = i;
        if(deq[stanga] == i - k)
            stanga++;
        if(i >= k)
            suma += v[deq[stanga]];
    }
    g<<suma;
    return 0;
}