#include<fstream>
using namespace std;
ifstream f("muzeu.in");ofstream g("muzeu.out");
int n,x[101][101],maxim;
void mergi(int i,int j,int t){int k;if(i<=n){if(i==n) if(maxim<t) maxim=t;for(k=0;k<3;k++)  mergi(i+1,j+k,t+x[i][j]);}}
int main(){int i=0,j=0,a=1,b=0,l,ok=1;f>>n;
while(f>>l){if(a==n+1/2) ok=0;
			if(b<a){x[i][j++]=l;b++;}
			else if(ok){a+=2;i++;j=0;x[i][j++]=l;b=1;}
				 else{a-=2;i++;j=0;x[i][j++]=l;b=1;}}
mergi(0,0,x[0][0]);g<<maxim;f.close();g.close();return 0;}