#include <fstream>
#include <deque>
#define M 5000000

using namespace std;

int s, n, k, a[M];
long long suma;

deque <int> D;

void citire()
{
    ifstream fin ("deque.in");
    fin >> n >> k;
    for (int i=0; i<n; i++)
        fin >> a[i];
}

void coada()
{
    for (int i=0; i<n; i++)
    {
        while (!D.empty() && a[i]<a[D.back()])
            D.pop_back();
        D.push_back(i);
        if (D.front()<=i-k)
            D.pop_front();
        if (i>=k-1)
            suma+=a[D.front()];
    }
}

int main()
{
    ofstream fout ("deque.out");
    citire();
    coada();
    fout << suma << '\n';
    return 0;
}