#include <fstream>

using namespace std;

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

int n,k,i,v[5000001],d[5000001],p,u;
long long s;

int main()
{
    fin >> n >> k;
    for (i=1; i<=n; i++)
        fin >> v[i];
    p = u = 1;
    d[1] = 1;
    for (i=2; i<=n; i++)
    {
        while (p <= u && v[i] <= v[d[u]])
            u--;
        d[++u] = i;
        if (i-d[p] == k)
            p++;
        if (i >= k)
            s += v[d[p]];
    }
    fout << s;
    return 0;
}