#include <fstream>
#include <deque>

using namespace std;

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

deque<int>dq;

const int NMAX=1000000;
int v[5*NMAX+5];

int main()
{
    int i,n,k,st=0,dr=-1;
    long long s=0;
    fin>>n>>k;
    for(i=1;i<=n;i++)
        fin>>v[i];
    for(i=1;i<=n;i++)
    {
        if(!dq.empty() && dq.front()==i-k)
            dq.pop_front();
        while(!dq.empty() && v[dq.back()]>=v[i])
            dq.pop_back();
        dq.push_back(i);
        if(i>=k)
        {
            s=s+v[dq.front()];
        }
    }
    fout <<s<<"\n";
    return 0;
}