#include <fstream>

using namespace std;

ifstream cin("deque.in");
ofstream cout("deque.out");


int main()
{
    int n, k;
    cin>>n>>k;
    int v[n+1];
    for(int i = 1; i <= n; i++)
        cin>>v[i];
    int sol = 0;
    int deque[n+1];
    int end = -1, front = 0;
    for(int i = 1;i <=n; i++)
    {
        while(end!= -1 && v[i] < v[deque[end]])
            end -= 1;
        if (end == -1)
            end = 0;
        end += 1;
        deque[end] = v[i];
        if (deque[front] <= i - k)
            front++;
        if (i >= k)
            sol += deque[front];
    }
    cout<<sol;
	return 0;
}