#include <bits/stdc++.h>
using namespace std;
#define maxn 5000010
int N,K;
int A[maxn], deq[maxn];
int front, back;
long long Sum;
int main()
{
ifstream f("deq.in");
ofstream g("deq.out");
int i;
cin >> N >> K;
for(i=1;i<=N;i++)
	cin >> A[i];
front = 1, back = 0; 	// front>back => deq vid
for(i=1;i<=N;i++)
{
	while(front<=back && A[i] <= deq[back])
		back--;
	deq[++back] = i;
	if(deq[front] == i-K)
		front++;
	if(i>=K)
		Sum += A[deq[front]];
}
g<<Sum;
f.close();
g.close();
return 0;
}