#include <fstream>
using namespace std;

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

struct nod
{ int val;
  int poz;
};

nod st[5000001];

int n, k, x, top, pr;
long long sum;

int main()
{
    int i;

    fin >> n >> k;
    fin >> x;

    pr = 1;
    top = 1;
    st[1].val = x;
    st[1].poz = 1;

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

        fin >> x;
        if(i - st[pr].poz + 1 > k) pr++;
        while(x < st[top].val && top >= pr) top--;

        top++;
        st[top].val = x;
        st[top].poz = i;
        if(i >= k) sum += st[pr].val;
       }

    fout << sum;

    return 0;
}