#include<bits/stdc++.h>
#define FILE "read"
#define MAXN 100010
using namespace std;
typedef long long ll;
ll n,k,head,tail,a[MAXN],sum[MAXN],f[MAXN],q[MAXN];
inline int read(){
	int x=0,f=1;  char ch=getchar();
	while(!isdigit(ch))  {if(ch=='-')  f=-1;  ch=getchar();}
	while(isdigit(ch))  {x=x*10+ch-'0';  ch=getchar();}
	return x*f;
}
int main(){
	freopen(FILE".in","r",stdin);
	freopen(FILE".out","w",stdout);
	n=read();  k=read();
	for(int i=1;i<=n;++i)  a[i]=read(),sum[i]=sum[i-1]+a[i];
	for(int i=1;i<=n;++i){
		while(head<tail&&i-q[head]-1>k)  ++head;
		if(i<=k)  f[i]=sum[i];
		else f[i]=f[q[head]]+sum[i]-sum[q[head]+1];
		while(head<tail&&f[i]-sum[i+1]>=f[q[tail]]-sum[q[tail]+1])  --tail;
		q[++tail]=i;
	}
	printf("%lld\n",f[n]);
	return 0;
}