#include <fstream>
#include <deque>

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

deque <int> d;
int i,n,v[5000001],k,rez=0;

int main()
{
    f>>n>>k;
    for (i=1; i<=n; ++i)
    {
        f>>v[i];
        while (!d.empty() && v[d.back()]>v[i])
        d.pop_back();
        d.push_back(i);
        if (d.front()<=i-k) d.pop_front();
        if (i>=k) rez+=v[d.front()];
    }
    g<<rez<<'\n';
    return 0;
}