#include<fstream>
#include<deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int N,i,k;
long long S;
int V[5000010];
deque <int> D;
int main(){


    fin>>N>>k;



    for(i=1;i<=N;i++){

        fin>>V[i];

        while(D.empty()==0 && V[i]<=V[D.back()]){
            D.pop_back();
        }

        D.push_back(i);

        if(D.front()==i-k)
            D.pop_front();
        if(i>=k)
            S+=V[D.front()];
    }

        fout<<S;


    return 0;
}