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

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

inline void Citire()
{
    int i;
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%d%d",&n,&k);
    for (i=1;i<=n;i++)
        scanf("%d",&a[i]);
}

inline void Rezolva()
{
    int i,minim=11000000,poz,pr,ul;
    pr=1;ul=0;
    for (i=1;i<=k;i++)
        {
            while (ul>=pr && a[i]<=deq[ul])
                    ul--;
            deq[++ul]=a[i];
            if (a[i]<minim)
                minim=a[i];
        }
    suma=suma+minim;
    //sort ( deq + 1 , deq + 1 + k );
    for (i=k+1;i<=n;i++)
         {
             while (ul>=pr && a[i]<=deq[ul])
                    ul--;
            deq[++ul]=a[i];
             if (a[i-k]==deq[pr])
                pr++;
             suma+=deq[pr];
         }
    printf("%lld",suma);
}

int main()
{
    Citire();
    Rezolva();
    return 0;
}