#include <iostream>
#include <fstream>
#include <queue>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k;
deque< pair<int,int> > q;


int main()
{
    f>>n>>k;
    int a;
    for(int i=1;i<k;i++)
    {
        f>>a;
        while(!q.empty())
            if(q.back().first>a)
                q.pop_back();
            else
                break;
        q.push_back(make_pair(a,i));
    }
    int s=0;
    for(int i=k;i<=n;i++)
    {
        f>>a;
        while(!q.empty())
            if(q.back().first>a)
                q.pop_back();
            else
                break;
        q.push_back(make_pair(a,i));
        if(q.front().second<=i-k)
            q.pop_front();
        s+=q.front().first;
    }
    g<<s;
    return 0;
}