#include <fstream>
#include <deque>

using namespace std;

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

int main()
{
    int n, k, x, sum=0;
    deque<pair<int, int>> d;
    fin>>n>>k;
    for (int i=0;i<n;++i)
    {
        fin>>x;
        while (!d.empty() && d.back().first>x)
            d.pop_back();
        d.push_back(make_pair(x, i));
        if (d.front().second+k==i)
            d.pop_front();
        if (i>=k-1)
            sum+=d.front().first;
    }
    fout<<sum;
    fin.close();
    fout.close();
    return 0;
}