#include<iostream>
#include<cstdio>
#include<cctype>
using namespace std;
inline void in(int &x){
    x=0;int f=1;char t=getchar();
    while(!isdigit(t)){if(t=='-')f=-1;t=getchar();}
    while(isdigit(t)){x=x*10+t-48;t=getchar();}
    x*=f;
}
const int maxn=10e4+10;
int n,m;
int a[maxn],f[maxn];
inline void dpwork(){
	for(int i=2;i<=n;i++){
		f[i]=f[i-1];
		for(int j=1;j*2<=min(m,i);j++)
			f[i]=max(f[i],f[i-j*2]+a[i-j]-a[i-j*2]);
	}
	printf("%d",f[n]);
}
inline void work(){
	in(n);in(m);m*=2;
	for(int i=1;i<=n;i++) in(a[i]),a[i]+=a[i-1];
	dpwork();
}
inline int mian(){
    freopen("cowrun.in","r",stdin);
	freopen("cowrun.out","w",stdout);
	work();
}
int Rose=mian();
int main(){;}