#include<stdio.h>
#define MAX 5000001

int V[MAX],D[MAX],n,F,B,k;
long long suma;

int main(){

freopen("deque.in","rt",stdin);
freopen("deque.out","wt",stdout);

scanf("%d%d",&n,&k);int i;
for(i=1;i<=n;i++) scanf("%lld",&V[i]);
F=1;B=0;
for(i=1;i<=n;i++){
	for(;F<=B && V[i]<=V[D[B]];) B--;
	D[++B]=i;
	if(D[F]==i-k) F++;
	if(i>=k)suma+=V[D[F]];
}printf("%lld\n",suma);
return 0;
}