#include<bits/stdc++.h>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n, k;
int v[5000001];
long long s;
int main()
{
	fin >> n >> k;
	for(int i=1; i<=n; i++) 
        fin >> v[i];
    deque<int>dq;
	for(int i=1; i<=n; i++)
	{
		while(!dq.empty() && v[i]<=v[dq.back()]) 
		    dq.pop_back();
		dq.push_back(i);
		if(dq.front()==i-k) 
		    dq.pop_front();
		if(i>=k)
		    s+=v[dq.front()]; 	
	}
	fout << s;
	return 0;
}