#include <iostream>
#include <fstream>

using namespace std;

int n,k;
int a[5000002],deque[5000002];
int front,back;
long long sum = 0;

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

int main ()
{
    fin >> n >> k;
    front  = 1; back = 0;
    for (int i = 1; i <= n; i++)
    {
        fin >> a[i];
        while (front <= back && a[i] <= a[deque[back]]) back--;
        deque[++back] = i;
        if (deque[front] == i - k) front++;
        if (i >= k) sum += a[deque[front]];
    }
    fout << sum;
    return 0;
}