#include <fstream>
#include <deque>

using namespace std;
const int NMAX=5000005;

ifstream fin("deque.in");
ofstream fout("deque.out");

deque < int > DQ;
long long V[NMAX],N,M,SUMA=0;

int main()
{
    fin>>N>>M;
 for (int i=1; i<=N; i++)
    fin>>V[i];
 for (int i=1; i<=N; i++)
 {
     while (!DQ.empty()&&V[i]<V[DQ.back()])
        DQ.pop_back();
     DQ.push_back(i);
     if (DQ.front()==i-M)
        DQ.pop_front();
     if (i>=M)
        SUMA+=V[DQ.front()];
 }
    fout<<SUMA<<"\n";
    return 0;
}