#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k,v[5000001],s,i;
deque <int> d;
int main()
{
    f>>n>>k;
    for(i=1;i<=n;i++)
    {
        f>>v[i];
    }
    for(i=1;i<=n;i++)
    {
        while(!d.empty() && v[i]<=v[d.back()])
        {
            d.pop_back();
        }
        d.push_back(i);
        while(d.front()<=i-k)
        {
            d.pop_front();
        }
        if(i>=k)
        {
            s=s+v[d.front()];
        }
    }
    g<<s;
    return 0;
}