#include <fstream>
#include <deque>
using namespace std;
const int NMAX=5e6;
int n, k, v[NMAX+3];
deque <int> dq;
long long sol;
int main()
{
    ifstream fin ("deque.in");
    ofstream fout ("deque.out");
    fin>>n>>k;
    for(int i=1; i<=n; i++)
        fin>>v[i];
    for(int i=1; i<=n; i++)
    {
        while(!dq.empty() && v[i]<=v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if(i>=k)///exista o subsecventa valida
            sol+=v[dq.front()];
        if(i-dq.front()+1==k)
            dq.pop_front();
    }
    fout<<sol;


    return 0;
}