#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
const int inf = 1e7;
const int maxn = 1e3+5;
int ma[maxn][maxn];
int line[maxn];
bool vis[maxn][maxn];
int x[5], y[5];
int n;
void make_table() {
	x[1] = 1; y[1] = 0;
	x[2] = 0; y[2] = 1;
	x[3] = -1; y[3] = 0;
	x[4] = 0; y[4] = -1;
}
bool judge(int nowx, int nowy, int tmax, int tmin) {
	if(nowx == n && nowy == n) return true;
	vis[nowx][nowy] = true;
	int tx, ty;
	for(int i = 1; i <= 4; i++) {
		tx = nowx+x[i]; ty = nowy+y[i];
		if(tx > n || ty > n || tx < 1 || ty < 1) continue;
		if(vis[tx][ty]) continue;
		if(ma[tx][ty] < tmin || ma[tx][ty] > tmax) continue;
		if(judge(tx, ty, tmax, tmin)) return true;
	}
	return false;
}
void read() {
	scanf("%d", &n);
	for(int i = 1; i <= n; i++) {
		for(int j = 1; j <= n; j++) {
			scanf("%d", &ma[i][j]);
			line[j+(i-1)*n] = ma[i][j];
		}
	}
} 
void solve() {
	int tmax, tmin;
	int ans = inf;
	for(int i = 1; i <= n*n; i++) {
		for(int j = 1; j <= n*n; j++) {
			if(line[j]-line[i] < 0) continue;
			if(line[j]-line[i] >= ans) continue;
			memset(vis, 0, sizeof(vis));
			if(judge(1 ,1 , line[j], line[i])) ans = line[j]-line[i];
		}
	}
	printf("%d", ans);
}
int main() {
	freopen("adven.in", "r", stdin);
	freopen("adven.out", "w", stdout);
	read();
	make_table();
	solve();
	return 0;
}