#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 deque[n + 1];
    int left = 0, right = -1;
    int sol = 0;
    for (int i = 1; i <= n; i++)
    {
        while(right != -1 && left <= right && v[i] <= v[deque[right]])
            right -= 1;
        right += 1;
        deque[right] = i;

        if (deque[left] == i - k)
            left += 1;
        if (i >= k)
            sol += v[deque[left]];
    }
    cout<<sol;
	return 0;
}