没有文件读入

#include<bits/stdc++.h>
using namespace std;
int n, i, j, l, k, x, y, s;
int d[55][55], f[55][55][55][55];
int main() {
	cin>>n;
	while(cin>>x>>y>>s && x)
		d[x][y] = s;
	for(i = 1; i <= n; i++)
		for(j = 1; j <= n; j++)
			for(l = 1; l <= n; l++)
				for(k = 1; k <= n; k++) {
					f[i][j][l][k] = max(max(f[i - 1][j][l - 1][k], f[i][j - 1][l][k-1]), max(f[i - 1][j][l][k - 1], f[i][j - 1][l - 1][k])) + d[i][j];
					if(i != 1 && j != k) f[i][j][l][k] += d[l][k];
				}
	printf("%d", f[n][n][n][n]);
	return 0;
}