#include <fstream>
#include <deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
long long n,k,i,j,minim;
struct el
{
    long long v,cnt;
};
el p;
deque <el> q;
int main()
{
    f>>n>>k;
    f>>p.v;
    q.push_back(p);
    for(i=1;i<k;i++)
    {
        f>>p.v;
        for(j=q.size()-1;j>=0;j--)
        {
            q[j].cnt++;
            if(q[j].v>p.v) q.pop_back();
        }
        q.push_back(p);
    }
    minim+=q[0].v;
    for(i=k;i<n;i++)
    {
        f>>p.v;
        for(j=q.size()-1;j>=0;j--)
        {
            q[j].cnt++;
            if(q[j].v>p.v) q.pop_back();
        }
        q.push_back(p);
        if(q[0].cnt>k-1) q.pop_front();
        minim+=q[0].v;
    }
    g<<minim;
    return 0;
}