#include<fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int v[5000001],d[5000001],i,p,u,n,k;
long long sum;
int main(){
    fin>>n>>k;
    for(i=1;i<=n;i++){
        fin>>v[i];
    }
    p=1;
    u=1;
    d[1]=1;
    for(i=2;i<=n;i++){
        while(p<=u && v[i]<v[d[u]]){
            u--;
        }
        d[++u]=i;
        if(i-d[p]==k){
            p++;
        }
        if(i>=k){
            sum+=v[d[p]];
        }
    }
    fout<<sum<<"\n";
    return 0;
}