#include<fstream>
#include<vector>
#include<queue>
#define N 5000001

using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

deque<long long>deq;
long long n,i,x,a[N],K;

int main()
{	fin>>n>>K;
	for(i=1;i<=n;i++)fin>>a[i];
	for(i=1;i<=n;i++)
	{	while(!deq.empty()&&a[i]<=a[deq.back()]) deq.pop_back();
		deq.push_back(i);
		if(deq.front()==i-K) deq.pop_front();
		if(i>=K)x+=a[deq.front()];
	}
	fout<<x<<'\n';
	return 0;
}