#include<fstream>
#include<deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int a[5000004],n,k,i;
deque <int> c;
long long solutie;
int main()
{
    fin>>n>>k;
    for(i=1;i<=n;++i)
    {
        fin>>a[i];
    }
    for(i=1;i<=k;++i)
    {
        while(c.size()>0&&a[i]<=a[c.back()])
        {
            c.pop_back();
        }
        c.push_back(i);
    }
    solutie=solutie+a[c.front()];
    for(i=k+1;i<=n;++i)
    {
        while(a[i]<=a[c.back()]&&c.size()>0)
        {
            c.pop_back();
        }
        c.push_back(i);
        if(i-c.front()>=k)
        {
            c.pop_front();
        }
        solutie=(long long)solutie+a[c.front()];
    }
    fout<<solutie;
    fin.close();
    fout.close();
    return 0;
}