#include<fstream>
#include<deque>
using namespace std;

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


deque<int> q;

int v[5000010];

int main()
{
	int n,k;
	long long sum=0;
	
	fin>>n>>k;
	
	for(int i=1;i<=n;i++)
		fin>>v[i];
		
	for(int i=1;i<=n;i++)
	{
		while(!q.empty() && v[i]<=v[q.back()]) q.pop_back();
        q.push_back(i);
        if(q.front()<=i-k) q.pop_front();
        if(i>=k) sum+=v[q.front()];
	}
	
	fout<<sum;
	
	return 0;
	
}