# include <fstream>
# define DIM 5000010
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int d[DIM];
long long s,p,k,u,i,n,v[DIM];
int main () {
    fin>>n>>k>>v[1];
    u=1;
    p=1;
    d[1]=1;
    for(i=2;i<=n;i++){
        fin>>v[i];
        while(v[i]<=v[d[u]]&&u>=p)
            u--;
        d[++u]=i;
        if(i-d[p]==k)
            p++;
        if(i>=k)
            s+=v[d[p]];
    }
    fout<<s<<"\n";
    return 0;
}