#include <iostream>
#include<fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
long n,k,v[5000001],d[5000001];
int i,suma=0,j,q;
int main()
{
    f>>n>>k;
    i=1;
    j=0;
    for(q=1;q<=n;q++)
        f>>v[q];
    for(q=1;q<=n;q++)
    {
        while(i<=j&&v[q]<=v[d[j]]) j--;
        j++;
        d[j]=q;
        if(d[i]==q-k) i++;
        if(q>=k) suma=suma+v[d[i]];
    }
    g<<suma;
    return 0;
}