#include<fstream>
#include<deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int v[5000001],n,k;
long long s=0;
deque<int>d;
int main()
{
    fin>>n>>k;
    for(int i=1;i<=n;++i)
        fin>>v[i];
    for(int i=1;i<=n;++i)
    {
        while(d.empty()==false&&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;
}