#include<stdio.h>

int n,k,v[5000100],d[5000100],p,u,i;
long long s;

int main(){
	FILE*f=fopen("deque.in","r");
	FILE*g=fopen("deque.out","w");
	
	fscanf(f,"%d %d",&n,&k);
	
	for(i=1;i<=n;i++)
		fscanf(f,"%d",&v[i]);
	
	p=1;u=0;
	for(i=1;i<=n;i++){
		while(p<=u && v[i]<=v[d[u]])
			u--;
		d[++u]=i;
		if(d[p]==i-k)
			p++;
		if (i >= k)
			s += v[d[p]];
		//fprintf(g,"%d ",d[p]);
	}
	
	fprintf(g,"%lld",s);
	fclose(f);fclose(g);
	return 0;
}