#include<fstream>
#include<deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n,i, a[5000005],k;
long long solutie=0;
int main()
{
    deque <int> indice;
    fin>>n>>k;
    for(i=1;i<=k;i++)
    {
        fin>>a[i];
        while(indice.size()>0&&a[i]<a[indice.back()])
        {
            indice.pop_back();
        }
        indice.push_back(i);
    }
    solutie=solutie+a[indice.front()];
    for(i=k+1;i<=n;i++)
    {
       fin>>a[i];
        while(indice.size()>0&&a[i]<a[indice.back()])
        {
            indice.pop_back();
        }
        indice.push_back(i);
        if(i-indice.front()==k)
        {
            indice.pop_front();
        }
        solutie=solutie+a[indice.front()];
    }
    fout<<solutie;
    fin.close();
    fout.close();
    return 0;
}