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