#include<iostream>
#include<fstream>
#include<cstdio>
#include<cmath>
#include<algorithm>
#include<ctime>
using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

int n,a[5000005],k,deq[5000005];
long long suma;

inline void Rezolva()
{
    int i,minim=1000000000,poz,pr,ul;
    deq[1]=a[1];
    pr=1;ul=1;
    for (i=2;i<=k;i++)
        {
            while (deq[ul]>a[i] && ul>=pr)
                ul--;
            deq[++ul]=a[i];
        }
    suma=suma+deq[1];
    for (i=k+1;i<=n;i++)
         {
             while (deq[ul]>a[i] && ul>=pr)
                ul--;
             deq[++ul]=a[i];
             if (a[i-k]==deq[pr])
                pr++;
             suma+=deq[pr];
         }
    fout<<suma<<"\n";
}

int main()
{
    int i;
    fin>>n>>k;
    for (i=1;i<=n;i++)
        fin>>a[i];
    Rezolva();
    return 0;
}