#include <fstream>
#include <deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n, m, i, j, k, x, ind;
long long s;
    deque <int> v;
    deque <int> poz;
int main()
{
    fin>>n>>k;
    for(i=0;i<n;i++)
        {
            fin>>x;
            while(poz.size()!=0&&poz.front()<=i-k)
            {
                v.pop_front();
                poz.pop_front();
            }
            while(poz.size()!=0&&v.back()>=x)
            {
                v.pop_back();
                poz.pop_back();
            }
            v.push_back(x);
            poz.push_back(i);
            if(i>=k-1)
                s+=v.front();
        }
    fout<<s<<'\n';
    return 0;
}