#include <iostream>



#include <fstream>







using namespace std;







int dq[5000005];







int main()



{



    ifstream in ("deque.in");



    ofstream out("deque.out");



    int n,k;



    in>>n>>k;



    long long v[n+5];



    for (int i=0;i<n;i++)



    {



        in>>v[i];



    }



    int st=0,dr=-1;



    long long s=0;



    for (int i=0;i<n;i++)



    {



        if (i>=k && dq[st]==i-k)



            st++;



        while(st<=dr && v[i]<=v[dq[dr]])



        {



            dr--;



        }



        dq[++dr]=i;



        if (i>=k-1) s+=v[dq[st]];



    }



    out<<s;



    in.close();



    out.close();



    return 0;



}