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

long long v[5000001];
long long sol=0;
deque <int> dq;
int main()
{
    int n, i, k;
    fin>>n>>k;
    for(i=1;i<=n;i++)
    {
        fin>>v[i];
    }
    dq.push_back(1);
    for(i=2;i<=n;i++)
    {
        while(v[i]<=v[dq.back()]&&!dq.empty())
        {
            dq.pop_back();
        }
        dq.push_back(i);
        if(dq.front()==i-k)
        {
            dq.pop_front();
        }
        if(i>=k)
        {
            sol=1ll*sol+v[dq.front()];
        }
    }
    fout<<sol;
}