#include <fstream>
#include <deque>
#include <algorithm>
using namespace std;
ifstream in ("deque.in");
ofstream out ("deque.out");
int v[5000001];
int main ()
{
    deque <long long> d;
    long long  n,k,p,s=0,a=0;
    in>>n>>k;
    for (int i=1;i<=n;++i)
        in>>v[i];
    for (int i=1;i<=n;++i)
    {
        p=v[i];
        while ( d.empty()==0 && v[d.back()]>p)
                d.pop_back();
        d.push_back(i);
        if (i-k==d.front())
            d.pop_front();
        if (i>=k)
            s+=v[d.front()];
    }
    out<<s;
    return 0;


}