//Deque

#include <fstream>
#define MAXN 5000050
using namespace std;
int n,k,a[MAXN],deque[MAXN];
long long suma;
int main()
{
    int i,front,back;
    ifstream f("deque.in");
    ofstream g("deque.out");
    f>>n>>k;
    for(i=1;i<=n;i++)
     f>>a[i];
    front=1,back=0; //deque vid initial
    for(i=1;i<=n;i++)
    {
     while(front<=back && a[i]<a[deque[back]]) back--;
     deque[++back]=i;
     if(deque[front]==i-k) front++;
     if(i>=k) suma+=a[deque[front]];
    }
    g<<suma<<"\n";
    f.close();
    g.close();
    return 0;
}