#include <iostream>
#include <fstream>
using namespace std;

int N,K,A[5000010],Deque[5000010],Front,Back;
long long sum;


int main()
{


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


    int i;
    fin>>N>>K;

    for (i=1;i<=N;i++)
        fin>>A[i];

    Back = 0;
    Front = 1;


    for (i=1;i<=N;i++)
    {
        while ( Front <= Back && A[i] <= A[Deque[Back]] )
            Back--;

        Back++;
        Deque[Back] = i;

        if (Deque[Front] == i-K)
            Front++;

        if (i>=K)
        {
            sum += A[Deque[Front]];
        }
    }

    fout<<sum;

    fin.close();
    fout.close();
    return 0;
}