#include<fstream>
#include<set>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n,k,i, v[5000010];
long long suma;
multiset<int> s;
multiset<int>::iterator it;

int main()
{
	fin>>n>>k;
	for(i=1;i<=n;i++)
		fin>>v[i];
	for(i=1;i<=k;i++)
	{
		s.insert(v[i]);
	}

	it = s.begin();
	suma += *it;
	for(i=k+1;i<=n;i++){
		s.insert(v[i]);
		s.erase(v[i-k]);
		it=s.begin();
		suma +=*it;
	}
	fout<<suma;
	return 0;
}