#include <fstream>
#include <deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");

deque<int>d;
long long n,k,s,i,a[5000100];
int main()
{
    f>>n>>k;
    for(i=1;i<=n;i++)f>>a[i];

    for(i=1;i<=n;i++)
    {
        while(!d.empty()&&a[i]<=a[d.back()])
        {
            if(d.size()==0)break;
            d.pop_back();
        }
        d.push_back(i);

        if(i-d.front()>=k)d.pop_front();


        if(i>=k)s=s+a[d.front()];

    }
    g<<s;

    return 0;
}