#include <fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int N, K, A[5000001], deq[5000001], Front, Back;
long long Suma;

int main(){
    Suma=0;
    fin>>N>>K;
    for(int i=1; i<=N; i++){
        fin>>A[i];
    }
    Front=1; Back=0;
    for(int i=1; i<=N; i++){
        while(Front<=Back && A[i]<=A[deq[Back]]){
            Back--;
        }
        Back++;
        deq[Back]=i;
        if(deq[Front]==i-K) Front++;
        if(i>=K) Suma=Suma+A[deq[Front]];
    }
    fout<<Suma;
    return 0;
}