#include<stdio.h>
int n,k,d[2][500010];
int main()
{
	FILE*f=fopen("deque.in","r");
	fscanf(f,"%d%d",&n,&k);
	int i,front,back,val,ok;
	long long s=0;
	for(i=front=back=0;i<n;++i)
	{
		fscanf(f,"%d",&val);
		while(front<=back&&val<=d[1][back])
			{--back;}
		if(i)++back;
		d[0][back]=i;
		d[1][back]=val;
		
		if(i-k>=d[0][front])
			++front;
		
		if(i>=k-1)
		{
			s+=d[1][front];
		}
	}
	fclose(f);
	FILE*g=fopen("deque.out","w");
	fprintf(g,"%lld\n",s);
	fclose(g);
	return 0;
}