#include <iostream>
#include <cstdio>
using namespace std;
#include <deque>
int n,x,l,i,k,y,j;
int main()
{
    deque<int> a,b;
    freopen("secventa.in","r",stdin);
    freopen("secventa.out","w",stdout);
    cin>>n>>k;
    cin>>x;
    a.push_back(x);
    b.push_back(1);
    l=1;
    for (i=1;i<k;i++)
    {
        cin>>x;
        while (x<=a[l-1]&&l>0)
        {
            a.pop_back();
            b.pop_back();
            l--;
        }
        a.push_back(x);
        b.push_back(i+1);
        l++;
    }
    y=a[0];

    for (i=k;i<n;i++)
    {  /* cout<<i<<" ";
        for (j=0;j<l;j++)
        {
            cout<<"("<<a[j]<<" , "<<b[j]<<") ";
        }
        cout<<'\n';
    */    cin>>x;
        if (i-b[0]==k-1)
        {
            l--;
            a.pop_front();
            b.pop_front();
        }

        while (x<=a[l-1]&&l>0)
        {
            a.pop_back();
            b.pop_back();
            l--;
        }
        a.push_back(x);
        b.push_back(i+1);
        l++;
        y+=a[0];

    }
   /*  for (j=0;j<l;j++)
        {
            cout<<"("<<a[j]<<" , "<<b[j]<<") ";
        }*/
   cout<<y;
}