#include<iostream>
#include<algorithm>
using namespace std;

long long tmp,a[101][101],n;

bool loang(long long mmin,long long mmax)
{
	long long check[101][101] = {0};
	long long tkx[4] = {-1,0,1,0};
	long long tky[4] = {0,1,0,-1};
	long long qx[101], qy[101];
	long long u,v,u1,v1;
	if (a[1][1]< mmin || a[1][1] > mmax)
	{
		return false;
	}
	qx[1] = 1;
	qy[1] = 1;
	long long first = 1;
	long long last = 1;
	check[1][1] = 1;

	while(first <= last)
	{
		u = qx[first];
		v = qy[first];
		first++;

		for(long long t = 0; t < 4; t++)
		{
			u1 = u + tkx[t];
			v1 = v + tky[t];
			if (u1>=1 && u1 <=n && v1>=1 && v1<=n && check[u1][v1]==0 && a[u1][v1]<=mmax&&a[u1][v1]>=mmin)
			{
				last++;
				qx[last] = u1;
				qy[last] = v1;
				check[u1][v1] = 1;
			}
		}


	}

	if(check[n][n] == 1) return true;
	return false;

}

int main()
{
	long long i,j;
	cin >> n;

	for(i = 1; i <= n; i++)
	{
		for(j = 1; j <= n; j++)
		{
			cin >> a[i][j];
		}
	}


	long long l=1,h=110,ans,m;
    while (l<=h)
    {
    	m =(l+h)/2;
    	bool ok= false;
    	for(long long mmin = 0; mmin <= 110; mmin++)
		{
	    	if(loang(mmin,mmin+m) == true)
	    	{
	    		ok= true;
				break;
			}
		}
		if(ok==true)
			{
				h = m - 1;
	    		ans = m;
			}
		else

		{

				l = m + 1;
		}
    }


    cout << ans;



}