#include<fstream>
#include<iostream.h>
using namespace std;
long c[5000001],a[5000001];

int main()
{ifstream f("deque.in");
ofstream g("deque.out");
long long n,i,k,p,u,s=0;
f>>n>>k;
p=1;u=0;
for(i=1;i<=n;i++)
{	f>>a[i];
	while(p<=u && a[i]<=a[c[u]])
		u--;
	
	u++;
	c[u]=i;
	
	if(c[p]==i-k)p++;
	if(i>=k) s=s+a[c[p]];
	     
}
g<<s<<'\n';
}