#include <fstream>
#include <deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");

int n;
int k;

long long s;

deque <int> q;

int v[5000001];



int main()
{
    fin>>n>>k;
    for(int i=1;i<k;i++)
    {
        fin>>v[i];
        while(q.empty()==false && v[i]<=v[q.back()])
        {
            q.pop_back();
        }
        q.push_back(i);
    }
    for(int i=k;i<=n;i++)
    {
        fin>>v[i];
        while(q.empty()==false && v[i]<=v[q.back()])
        {
            q.pop_back();
        }
        while(q.empty()==false && i-q.front()+1>k){
            q.pop_front();
        }

        q.push_back(i);
        s+=v[q.front()];
    }
    fout<<s;
}