#include<iostream>
#include<cstring>
#include<cstdio>
#include<string>
#include<algorithm>
#include<cmath>
#include<utility>
#include<stdio.h>
#include<cstdlib>
#include<iomanip>	//cout<<setiosflags(ios::fixed)<<setprecision(2);
#include<ctime> //double a=(double)clock();	cout<<a<<endl;
#include<vector>
#include<queue>
using namespace std;
const int ws_[4]={0,1,0,-1},ad_[4]={1,0,-1,0};
inline int read()
{
	int x=0,ff=1;char ch=getchar();
	while(ch>'9'||ch<'0'){if(ch=='-')ff=-1; ch=getchar();}
	while(ch<='9'&&ch>='0'){x=x*10+ch-'0';ch=getchar();}
	return ff*x;
}
int N,L,R,M,U,D;
int map[110][110];
bool vis[110][110];
void dfs(int x,int y)
{
	vis[x][y]=1;
	if(vis[N][N])
		return;
	for(int i=0;i<=3;i++)
	{
		int tx=x+ws_[i],ty=y+ad_[i];
		if(tx<=0||ty<=0||tx>N||ty>N)
			continue;
		if((!vis[tx][ty])&&map[tx][ty]<=U&&map[tx][ty]>=D)
			dfs(tx,ty);
	}
}
bool check(int X)
{
	for(D=0;D<=200-X;D++)
	{
		memset(vis,0,sizeof(vis));
		U=D+X;
		if(map[1][1]<=U&&map[1][1]>=D)
			dfs(1,1);
		if(vis[N][N])
			return 1;
	}
	return 0;
}
int main()
{
	freopen("adven.in","r",stdin);
	freopen("adven.out","w",stdout);
	N=read();
	for(int i=1;i<=N;i++)
		for(int j=1;j<=N;j++)
			map[i][j]=read();
	L=0,R=200;
	while(L+1<R)
	{
		M=(L+R)>>1;
		if(check(M))
			R=M;
		else
			L=M;
	}
	if(check(L))
		printf("%d\n",L);
	else
		printf("%d\n",R);
	return 0;
}