#include <fstream>
#include <deque>
#define MAX 5000001

using namespace std;

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

deque <int> v;
deque <int>::iterator ptr;

int a[MAX],n,k,c,*j;
long long s;


int main()
{
    f>>n>>k;
    for(int i=1; i<=n; ++i)
        f>>a[i];
    c=k,k=1-k;
    for(int i=1; i<=n; ++i)
    {
        while(!v.empty() && a[i]<=a[v.back()])
            v.pop_back();
        while(!v.empty() && v.front()<=k)
            v.pop_front();
        v.push_back(i),k++;
        if(i>=c)
            s+=a[v.front()];
    }
    g<<s;
    return 0;
}