#include<bits/stdc++.h>
#include<atcoder/all>
#define rep(i,n) for(int i=0;i<n;i++)
using namespace std;
using namespace atcoder;
typedef long long ll;
typedef vector<int> vi;
typedef vector<long long> vl;
typedef vector<vector<int>> vvi;
typedef vector<vector<long long>> vvl;
typedef long double ld;
typedef pair<int, int> P;

ostream& operator<<(ostream& os, const modint& a) {os << a.val(); return os;}
template <int m> ostream& operator<<(ostream& os, const static_modint<m>& a) {os << a.val(); return os;}
template <int m> ostream& operator<<(ostream& os, const dynamic_modint<m>& a) {os << a.val(); return os;}
template<typename T> istream& operator>>(istream& is, vector<T>& v){int n = v.size(); assert(n > 0); rep(i, n) is >> v[i]; return is;}
template<typename U, typename T> ostream& operator<<(ostream& os, const pair<U, T>& p){os << p.first << ' ' << p.second; return os;}
template<typename T> ostream& operator<<(ostream& os, const vector<T>& v){int n = v.size(); rep(i, n) os << v[i] << (i == n - 1 ? "\n" : " "); return os;}
template<typename T> ostream& operator<<(ostream& os, const vector<vector<T>>& v){int n = v.size(); rep(i, n) os << v[i] << (i == n - 1 ? "\n" : ""); return os;}

template<typename T> void chmin(T& a, T b){a = min(a, b);}
template<typename T> void chmax(T& a, T b){a = max(a, b);}

int main(){
	int h, w;
	cin >> h >> w;
	vector<vector<int>> a(h, vector<int>(w));
	cin >> a;
	using PQ = priority_queue<P, vector<P>, greater<P>>;
	PQ pq0;
	PQ pq1;
	pq0.emplace(0, 0);
	pq1.emplace(0, h * w - 1);
	int ans = -2;
	bool stop_flag = false;
	vector<int> dy = {1, 0, -1, 0};
	vector<int> dx = {0, 1, 0, -1};
	vector<vector<int>> col(h, vector<int>(w, -1));
	auto paint = [&](PQ& pq, int c){
		int tile = -1;
		int fy = -1;
		int fx = -1;
		while(true){
			auto p = pq.top(); pq.pop();
			tile = p.second;
			fy = tile / w;
			fx = tile % w;
			if(col[fy][fx] == -1) break;
		}
		col[fy][fx] = c;
		rep(t, 4){
			int ty = fy + dy[t];
			int tx = fx + dx[t];
			if(ty >= 0 and ty < h and tx >= 0 and tx < w){
				if(col[ty][tx] == -1){
					pq.emplace(a[ty][tx], ty * w + tx);
				}else{
					if(col[ty][tx] != c) stop_flag = true;
				}
			}
		}
		ans++;
	};
	while(true){
		paint(pq0, 0);
		if(stop_flag) break;
		paint(pq1, 1);
		if(stop_flag) break;
	}
	cout << ans << "\n";
	return 0;
}