#include <fstream>
#include <deque>

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