#include <fstream>

using namespace std;

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

long long a[5000005],i,n,k,p,u,d[5000005],s;

int main ()
{
    fin>>n>>k;
    for(i=1;i<=n;i++)
        fin>>a[i];
    p=u=d[1]=1;
    for(i=2;i<=n;i++)
    {
        while(a[i]<a[d[u]]&&p<=u)
            --u;
            d[++u]=i;
        if(i-d[p]==k)
            p++;
        if(i>=k)
            s+=a[d[p]];
    }
    fout<<s;
    return 0;
}