#include <fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n, h, Vect[5000001], dequ[5000001], Fr, Bk;
long long S;

int main(){
    S=0;
    fin>>n>>h;
    for(int i=1; i<=n; i++){
        fin>>Vect[i];
    }
    Fr=1; Bk=0;
    for(int i=1; i<=n; i++){
        while(Fr<=Bk && Vect[i]<=Vect[dequ[Bk]]){
            Bk--;
        }
        Bk++;
        dequ[Bk]=i;
        if(dequ[Fr]==i-h) Fr++;
        if(i>=h)
        {
             S=S+Vect[dequ[Fr]];
        }

    }
    fout<<S;
    return 0;
}