#include <iostream>
#include <algorithm>
using namespace std;
int a[55][55], f[55][55][55][55];
inline int read(){
	int x = 0, f = 1;
	char c = getchar();
	while(c < '0'  ||  c > '9'){
		if(c == '-')
			f =  - 1;
		c = getchar();
	}
	while(c >= '0'  &&  c <= '9'){
		x = x * 10 + c - 48;
		c = getchar();
	}
	return x * f;
}
int main(){
	int n = read(), x = read(), y = read(), z = read(); 
    while(x > 0  &&  y > 0  &&  z > 0){
        a[x][y] = z;
        cin >> x >> y >> z;
    }
    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++){
						int opt1 = max(f[i - 1][j][k - 1][l], f[i][j - 1][k][l - 1]);
	                    int opt2 = max(f[i - 1][j][k][l - 1], f[i][j - 1][k - 1][l]);
	                    f[i][j][k][l] = max(opt1, opt2) + a[i][j];
	                    if(i != k && j != l)
							f[i][j][k][l] += a[k][l];
					}
    cout << f[n][n][n][n] << '\n';
    return 0;
}