#include<fstream>
#include<deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int main()
{
    long long sum=0;
    int n,k,i,x;
    deque< pair<int, int> > dq;
    f>>n>>k>>x;
    if(k==1)sum=x;
    dq.push_back(make_pair(x,1));
    for(i=2;i<=n;++i)
    {
        f>>x;
        if(i-dq.front().second==k)dq.pop_front();
        while(!dq.empty() && x<=dq.back().first) dq.pop_back();
        dq.push_back(make_pair(x,i));
        if(i>=k) sum+=dq.front().first;
    }
    g<<sum<<"\n";
    f.close();
    g.close();
    return 0;
}