#include<stdio.h>
using namespace std;
FILE *f=fopen("deque.in","r");
FILE *g=fopen("deque.out","w");
long long s;
int v[500005],c[500005],n,k,i,u,p;
int main(){
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++){
	//mentinem ordinea crescatoare
	while(p<=u && v[i] <= v[c[u]] )
		 u--;
	//adaugam elem curent
	u++;
	c[u]=i;
	// minimul nu mai apartine secventei
	if(c[p]==i-k)
		p++;
	//adunam minimul la suma
	if (i>=k)
		s+=v[c[p]];
}
fprintf(g,"%lld",s);
return 0;
}