#include <iostream>
#include <fstream>
#include <deque>

using namespace std;

deque < long > q;
long a[5000010], n, k;
long long s=0;

int main()
{
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    fin >> n >> k;
    for (int i=1; i<=n; i++)
        fin >> a[i];
    for (int i=1; i<=n; i++)
    {
        if (!q.empty())
        {
            if (q.front()<i-k+1)
                q.pop_front();
            while(!q.empty())
                if (a[q.back()]>a[i])
                    q.pop_back();
                else
                    break;
        }
        q.push_back(i);
        if (i>=k)
            s+=a[q.front()];
    }
    fout << s;
    return 0;
}