#include <fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int v[5000010],d[5000010],n,p,u,i,k;
long long s;
int main(){
    fin>>n>>k;
    for(i=1;i<=n;i++)
    {
     fin>>v[i];
    }
    p=1;
    u=0;
    for(i=1;i<=n;i++)
    {
        while(p<=u&&v[i]<=v[d[u]])
        {
            u--;
        }
        d[++u]=i;
        if(d[p]==i-k)
            p++;
        if(i>=k)
            s+=v[d[p]];
    }
    fout<<s;





    return 0;
}