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





    return 0;
}