#include <fstream>

using namespace std;

int v[5000001], coada[5000001];


ifstream cin("deque.in");

ofstream cout("deque.out");

int main()

{

    int n, k, i;

    cin>>n>>k;

    for(i=1;i<=n;i++)

    {

        cin>>v[i];

    }

    int inc, sf;

    long long sum=0;

    inc=sf=1;

    coada[1]=1;

    for(i=2;i<=n;i++)

    {

        if(coada[inc]<i-k+1)

            inc++;

        while(inc<=sf&&v[i]<v[coada[sf]])

        {

            sf--;

        }

        sf++;

        coada[sf]=i;

        if(i>=k)

        {

            sum+=v[coada[inc]];

        }

    }

    cout<<sum;

    return 0;

}