#include<iostream>
#include<cstdio>
#include<cctype>
#define gys mylove
int n,x,y,z,a[51][51],dp[51][51][51][51];
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;
}
inline void input(){
	in(n);in(x);in(y);in(z);
	while(x&&y&&z){
		a[x][y]=z;
		in(x);in(y);in(z);
	}
}
inline void work(){
	for(int i=1;i<=n;i++)
	 for(int j=1;j<=n;j++)
	  for(int k=1;k<=n;k++)
	   for(int l=1;l<=n;l++){
	   	dp[i][j][k][l]=max(max(dp[i-1][j][k-1][l],dp[i][j-1][k][l-1]),max(dp[i-1][j][k][l-1],dp[i][j-1][k-1][l]))+a[i][j];
	   	if(i!=k&&j!=l) dp[i][j][k][l]+=a[k][l];
	   }
	printf("%d",dp[n][n][n][n]);
}
int Main(){
	freopen("fgqs.in","r",stdin);
	freopen("fgqs.out","w",stdout);
	input();
	work();
	return 0;
}
int main(){;}
int gys=Main();