#include<fstream>
#include<set>
#define x first
#define y second
#include<deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
deque<pair<int,int> >d;
int n,k,a;
long long r;
int main()
{
    fin>>n>>k;
    for(int i=1;i<=n;i++)
    {
        fin>>a;
        while(1)
        {
            if(!d.size())
                break;
            if(d.back().x<a)
                break;
            d.pop_back();
        }
        d.push_back({a,i});
        while(1)
        {
            if(!d.size())
                break;
            if(d.front().y>i-k)
                break;
            d.pop_front();
        }
        if(i>=k)
            r+=d.front().x;
    }
    fout<<r;
}