#include <iostream>
#include<fstream>
#include<deque>
using namespace std;
deque<long long>dq[3];
long long k,n,i,x,sum;
int main()
{
     ifstream f("deque.in");
     ofstream g("deque.out");
        f>>n>>k;
    for(i=1;i<=n;i++)
    {
        f>>x;
        while(!dq[0].empty() && x<=dq[0].back())
            {dq[0].pop_back(); dq[1].pop_back();}
        dq[0].push_back(x);
        dq[1].push_back(i);
        if(dq[1].front()==i-k)
            {dq[0].pop_front(); dq[1].pop_front();}
        if(i>=k)
        {
            sum+=dq[0].front();
        }
            }
           g<<sum;
}