// deque1.cpp : Defines the entry point for the console application.
//


#include<fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
#define maxn 5000010
int a[maxn],d[maxn];
int n,k;
int main()
{

int i,fi,b;
f>>n>>k;
long sum=0;
for(i=1;i<=n;i++)
	f>>a[i];
fi=1;b=0;
for(i=1;i<=n;i++)
{
	while(fi<=b && a[i]<=a[d[b]])b--;
 
	b++;
	d[b]=i;

	if(d[fi]==i-k)fi++;
	if(i>=k)sum+=a[d[fi]];
}
	g<<sum;

	
	return 0;
}