#include <fstream>
#include <deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
deque<int>q;
int v[5000005];
int main()
{
    long long s=0;
    int n, i, k;
    fin>>n>>k;
    for(i=1;i<=n;i++)
        fin>>v[i];
    for(i=1;i<=n;i++)
    {
        while(!q.empty() and v[i]<=v[q.back()])
            q.pop_back();
        q.push_back(i);
        if(q.front()==i-k)
            q.pop_front();
        if(i>=k)
            s=s+v[q.front()];
    }
    fout<<s<<"\n";
    return 0;
}