#include <fstream>

using namespace std;
int n,k,Min,a[5000005],coada[5000005],i,j,p,u;
long long s;
ifstream f("deque.in");
ofstream g("deque.out");
void citire()
{
    f>>n>>k;
    for(i=0;i<n;i++)
    {
        f>>a[i];
    }
}
int rezolvare()
{
    p=0;
    u=-1;
    for(i=0;i<n;i++)
    {
        if(coada[p]== i-k && p<=u)p++;
        while(u>=p)
            if(a[i]<=a[coada[u]]) u--;
            else break;
        coada[++u]=i;
        if(i>=k-1)
        {
            s+=a[coada[p]];
        }
    }
    return s;
}
int main()
{
    citire();
    g<<rezolvare()<<'\n';
    return 0;
}