#include <fstream>

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

    }
    fout<<s;
    return 0;
}