Zen

#include <fstream>
#include <deque>
using namespace std;
ifstream fin("zen.in");
ofstream fout("zen.out");
#define mp make_pair
#define f first
#define s second
deque <pair<long long,int> >q;
long long n,k,i,x;

int main()
{
    fin>>n>>k;
    q.push_back(mp(0,0));
    for(i=1;i<=n;++i)
    {
        fin>>x;
        while(q.size()&&q.front().s<i-k)
            q.pop_front();
        x+=q.front().f;
        while(q.size()&&q.back().f>=x)
            q.pop_back();
        q.push_back(mp(x,i));
    }
    fout<<x;
}