#include <fstream>
#include <set>
#define LE 5000007
#define ll long long
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
multiset <ll> S;
multiset<ll>::iterator it;
ll V[LE],k,m,Suma;
int main()
{
  ll n,i;
  f>>n>>m;

  for(i=1;i<=n;++i)
  {
      f>>V[i];
       if (i>m)
         S.erase(S.find(V[i-m]));

       S.insert(V[i]);
      if (i>=m)
      {
           it=S.begin();
           Suma+=*it;
      }
  }

g<<Suma<<'\n';

  f.close();
  g.close();
  return 0;
}