#include<stdio.h>
#define maxn 5000001
using namespace std;
int dq[maxn],poz[maxn];
int n,k;
long long s=0;
void deque_solve(){
	int x,f=1,b=0;
	for(int i=1;i<=n;i++){
		scanf("%d",&x);
		if(dq[f]>=x)
			b=f-1;
		else
		while(f<=b && dq[b]>=x)
			b--;
		dq[++b]=x;
		poz[b]=i;
		
		if(i>=k){
			if((i-poz[f])==k)
			++f;
			s+=dq[f];
		}
		
	}
}


int main(){
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	scanf("%d%d",&n,&k);
	deque_solve();
	printf("%lld",s);
	return 0;
}