#include <bits/stdc++.h>

using namespace std;
const int N=1010;
int a[N][N];
bool ch[1000010];
vector <int> v;
int mn=1e9;
int sx,sy,tx,ty;
int n;

bool area(int y,int x){
    return y>0&&y<=n&&x>0&&x<=n;
}

int dx[]={0,1,0,-1};
int dy[]={1,0,-1,0};
bool dfs(int f,int y,int x,bool visited[N][N]){
    if(y==ty&&x==tx) return true;
    if(visited[y][x]) return false;
    visited[y][x]=true;
    for(int d=0;d<4;++d){
        int i=y+dy[d],j=x+dx[d];
        if(area(i,j)&&a[i][j]<=f)
            if(dfs(f,i,j,visited)) return true;
    }
    return false;
}

void bsearch(int l,int r){
    while(l<=r){
        int m=(l+r)/2;
        bool visited[N][N]={};
        if(dfs(v[m],sy,sx,visited)){
            r=m-1;
            mn=min(mn,v[m]);
        }else
            l=m+1;
    }
}

int main()
{
    scanf("%d",&n);
    bool c=true;
    for(int i=1;i<=n;++i){
        for(int j=1;j<=n;++j){
            scanf("%d",&a[i][j]);
            if(!ch[a[i][j]] && a[i][j]){
                v.push_back(a[i][j]);
                ch[a[i][j]]=true;
            }
            if(c&&!a[i][j]){ sy=i; sx=j; c=!c;}
            if(!c&&!a[i][j]){ ty=i; tx=j;}
        }
    }
    sort(v.begin(),v.end());
    bsearch(0,v.size()-1);
    printf("%d",mn);
    return 0;
}