#include<stdio.h>
#define maxn 5000010
FILE *f=fopen("deque.in","r"), *g=fopen("deque.out","w");
int n,i,prim,ultim,a[maxn],deque[maxn],k;
long long sum=0;
int main()
{
	fscanf(f,"%d %d",&n,&k);
	
	for(i=1;i<=n;i++) fscanf(f,"%d\n",&a[i]); 
	
	prim=1;
	ultim=0;
	
	for(i=1;i<=n;i++)
	{
		while(prim<=ultim && a[deque[ultim]]>=a[i]) ultim--;
		deque[++ultim]=i;
		
		if(i-k==deque[prim]) prim++;
		
		if(i>=k)sum+=a[deque[prim]];
	}
	
	fprintf(g,"%lld\n",sum);
	fclose(g);
	fclose(f);
	return 0;
}