#include <fstream>

#include <deque>

using namespace std;

ifstream fin("deque.in");

ofstream fout("deque.out");

deque <int> dq;

int main()

{

	int n,k,v[5000005];

	long long s=0;

	fin>>n>>k;

	for(int i=1;i<=n;i++)

		fin>>v[i];

	for(int i=1;i<=k;i++){

			while(!dq.empty() and v[dq.back()]>= v[i]){

						dq.pop_back();

			}

			dq.push_back(i);

}

s+=v[dq.front()];

	for(int i=k+1;i<=n;i++)

	{

		while(!dq.empty() and v[dq.back()]>=v[i])

			dq.pop_back();

		dq.push_back(i);

		while(!dq.empty() and dq.front()<i-k+1)

			dq.pop_front();

		s+=v[dq.front()];

	}

	fout<<s;

}