#include<fstream>
#include<deque>

using namespace std;
int i,n,j,k,x,y,a[5000100];
long long int s=0;
deque<int> d;


ifstream f("deque.in");
ofstream g("deque.out");

int main()
{
    f>>n>>k;
    for(i=1;i<=n;i++)
    {
        f>>a[i];
        while(!d.empty() && a[i]<=a[d.back()]){
            d.pop_back();
        }
        d.push_back(i);
        if(d.front()==i-k)
            d.pop_front();
        if(i>=k)
            s+=a[d.front()];

    }
    g<<s;

}