#include <iostream>
#include <fstream>
#include <deque>
using namespace std;

int main()
{
    int n,k;
    ifstream f ("deque.in");
    ofstream g ("deque.out");
    f>>n>>k;
    deque<int>t;
    deque<int>q;
    long int mx=0;
    for (int i=1; i<=n; i++){
        int x; f>>x;
        if (i-k>=q.front()){t.pop_front();q.pop_front();}
        while (t.size()>0&&x<=t.back()) { t.pop_back(); q.pop_back(); }
        t.push_back(x); q.push_back(i);

        if (i>=k)mx+=t.front();
    }
    g<<mx;
    return 0;
}