#include <fstream>
#define N_max 499999
using namespace std;
ifstream cin ("deque.in");
ofstream cout ("deque.out");
long long rmq[100][N_max],sum,k;
int E[N_max];
int n;
int main()
{
    cin>>n>>k;
    for(int i=1;i<=n;++i) cin>>rmq[0][i];
    for(int p=1;(1<<p)<=n;++p)
    {
        for(int i=1;i<=n;i++)
        {
            rmq[p][i]=rmq[p-1][i];
            int aux=i+(1<<(p-1));
            if(aux<=n && rmq[p-1][aux]<rmq[p][i]) rmq[p][i]=rmq[p-1][aux];
        }
    }
    E[1]=0;
    for(int i=2;i<=n;++i) E[i]=1+E[i/2];
    for(int i=1;i<=n-k+1;++i)
    {
        int dr=i+k-1;
        int e=E[dr-i+1];
        long long len=(1<<e);
        sum+=min(rmq[e][i],rmq[e][dr-len+1]);
    }
    cout<<sum;
}