#include <fstream>
#include <deque>

using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
deque<int>q;
int v[5000005];
int main()
{
    int n,k;
    cin>>n>>k;
    for(int i=1; i<=n; i++)
        cin>>v[i];
    for(int i=1; i<k; i++)
    {
        while(!q.empty() && v[i]<v[q.back()])
            q.pop_back();
        q.push_back(i);
    }
    long long s=0;
    for(int i=k; i<=n; i++)
    {
        while(!q.empty() && v[i]<v[q.back()])
            q.pop_back();
        while(!q.empty() && i-q.front()>=k)
            q.pop_front();
        q.push_back(i);
        //cout<<q.front()<<'\n';
        s+=v[q.front()];
    }
    cout<<s;
    return 0;
}