#include <fstream>
#include <deque>
using namespace std;
ifstream fin ("deque.in");
ofstream fout("deque.out");
int n,k,i;
long long S;
deque<int> D;
int V[5000010];
int main()
{

    fin>>n>>k;
    for(i=1;i<=n;i++)
        fin>>V[i];

    D.push_back(1);
    for(i=2;i<=n;i++)
    {
        while(!D.empty()&&V[i]<=V[D.back()])
            D.pop_back();

        D.push_back(i);

        if(i-D.front()==k)
            D.pop_front();

        if(i>=k)
            S=S+V[D.front()];
    }
    fout<<S;
    return 0;
}