#include <fstream>
#include <deque>

using namespace std;

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

int n, k, sir[5000005];
long long s;
deque <int> q;

int main()
{
    cin >> n >> k;
    for(int i = 1; i<=n; i++)
        {
            cin >> sir[i];
        }
    for(int i = 1; i<=n; i++)
    {
        while(!q.empty() && sir[i] <= sir[q.back()])
            q.pop_back();
        q.push_back(i);
        if(i >= k)
        {
            if(!q.empty() && q.front() == i - k)
                q.pop_front();
            s += sir[q.front()];
        }
    }
    cout << s;

    return 0;
}