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