#include <fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
struct de
{
    int x;
    int pos;
}deq[5000001];

long long s;
int i,n,sf,st,k,z;

int main()
{
    fin>>n>>k;
    sf=1; st=1;
    fin>>deq[1].x; deq[1].pos=1;
    for (i=2;i<=n;i++)
    {
        fin>>z;
        while (z<=deq[sf].x&&st<=sf) sf--;
        deq[++sf].x=z; deq[sf].pos=i;
        if (i>=k)
        {
        if(deq[st].pos<=i-k) st++;
        s=s+deq[st].x;
        }
    }
    fout<<s;
    return 0;
}