#include <fstream>
using namespace std;
int  v[50000001], D[5000001], i, n, k, p, u;
long long sol;
int main()
{
    ifstream fin ("deque.in");
    ofstream fout ("deque.out");
    fin>>n>>k;
    for (i=1; i<=n; i++)
        fin>>v[i];
    p=1;
    u=0;
    for (i=1; i<=n; i++)
    {
        while (p<=u && v[i]<=v[D[u]])
            u--;
        D[++u]=i;
        if (D[p]==i-k)
            p++;
        if (i>=k)
            sol+=v[D[p]];
    }
    fout<<sol;

}