#include <fstream>

using namespace std;

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

struct qq{long long val, id;};

qq deq[2500010];

long long n, k, i, bk, fr, x, sum;

int main()
{
    fin>>n>>k;
    fr=1; bk=0;
    deq[0].val=(-1)*1000000000000000;
    for (i=1; i<=n; i++)
    {
        fin>>x;
        while (bk>=fr && deq[bk].val>=x)
            bk--;
        deq[++bk].val=x;
        deq[bk].id=i;
        if (deq[fr].id==i-k)
            fr++;
        if (k<=i)
        {
            sum+=deq[fr].val;
        }
    }
    fout<<sum;
    return 0;
}