#include <fstream>
#define int long long
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n,k,v[5000005],d[5000005],st,dr,i,sum;
signed main()
{
    fin>>n>>k;
    for (int i=1;i<=n;i++)
    {
        fin>>v[i];
    }
    st=1;
    dr=1;
    d[dr]=1;
    for (int i=2;i<=n;i++)
    {
        while (v[i]<=v[d[dr]]&&dr>=0)
        {
            dr--;
        }
        d[++dr]=i;

        if (d[st]==i-k)
        {
            st++;
        } if (i>=k) sum+=v[d[st]];

    }
    fout<<sum;
    return 0;
}