#include <fstream>
#include <deque>
#define valoare first
#define indice second
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
long long sol;
int n,i,x,k;
deque <pair<int,int> > q;
int main()
{
    fin>>n>>k;
    for(i=1;i<k;i++)
    {
        fin>>x;
        while(q.size()&&x<=q.back().valoare)
            q.pop_back();
        q.push_back(make_pair(x,i));
    }
    for(i=k;i<=n;i++)
    {
        fin>>x;
        while(q.size()&&x<=q.back().valoare)
            q.pop_back();
        q.push_back(make_pair(x,i));
        if(q.front().indice==i-k)
            q.pop_front();
        sol+=q.front().valoare;
    }
    fout<<sol;
    return 0;
}