#include <cstdio>
using namespace std;
int i,n,a[5000001],deque[5000001],k,st,sf;
long long t,aux;
int main()
{
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	scanf("%ld%ld",&n,&k);st=1;sf=0;
	for(i=1;i<=k-1;i++){
		scanf("%ld",&a[i]);
		while((a[i]<a[deque[sf]])&&(st<=sf)){sf--;}
		deque[++sf]=i;
					 }
	for(i=k;i<=n;i++){
		scanf("%ld",&a[i]);
		while((a[i]<a[deque[sf]])&&(st<=sf)){sf--;}
		deque[++sf]=i;aux=a[deque[st]];t+=aux;
		if(deque[st]==i-k+1){st++;}
					 }
	printf("%I64d",t);
return 0;
}