#include <fstream>
#define nmax 5000010
using namespace std;
long long dq[nmax];
long long  v[nmax];
int main()
{
    ifstream f("deque.in");
    ofstream g("deque.out");
    int k,n,i,inc,sf;
    long long sum;
    f>>n>>k;
    for (i=1;i<=n;i++)
        f>>v[i];
    inc=1;sf=0;
    for (i=1;i<=k;i++)
    {
        while ( dq[sf]>v[i] && inc<=sf )
            sf--;
        dq[++sf]=v[i];
    }
    sum=dq[1];
    for (i=k+1;i<=n;i++)
    {
        while ( dq[sf]>v[i] && inc<=sf )
            sf--;
        dq[++sf]=v[i];
        if (dq[inc]==v[i-k]) inc++;
        sum+=dq[inc];
    }
    g<<sum<<'\n';
    f.close();
    g.close();
    return 0;
}