#include "bits/stdc++.h"

#include <stdio.h>
#include <math.h>

#include "atcoder/all"
#include <float.h>

//#include <boost/multiprecision/cpp_int.hpp>
//using namespace boost::multiprecision;

using namespace std;
using namespace atcoder;

using ll = long long;
using ull = unsigned long long;
using mint = modint998244353;
using mint2 = modint1000000007;
const double eps = 1e-9;

#define REP(i, n) for (ll i = 0; i < ll(n); ++i)
#define REPI(i, init, n) for (ll i = init; i < ll(n); ++i)
#define REPD(i, init) for (ll i = init; i >=0; --i)
#define REPDI(i, init, n) for (ll i = init; i >=n; --i)
#define REPE(i, c) for (const auto& i : c)
#define REPM(i, c) for (auto&& i : c)
#define TCASE() ll _ttt; cin >> _ttt; while(_ttt--)

using vl = vector<ll>; using vvl = vector<vl>; using vvvl = vector<vvl>;
#define VLI(a, n) vector<ll> a; a.assign(n, 0); for(auto& x : a) cin >> x;
#define DLI(a, n) deque<ll> a; a.assign(n, 0); for(auto& x : a) cin >> x;
#define VSI(a, n) vector<string> a; a.assign(n, ""); for(auto& x : a) cin >> x;
#define VVLI(a, n, m, init) vector<vector<ll>> a(n); for(auto& x : a) x.assign(m, init);
using vd = vector<double>; using pl = pair<ll, ll>; using vpl = vector<pl>;

struct uv { ll u; ll v; ll c; };
#define VUVI(a, n) vector<uv> a; a.assign(n, {0, 0, 1}); for(auto& x : a) {cin >> x.u >> x.v; x.u--; x.v--;}
#define VUVCI(a, n) vector<uv> a; a.assign(n, {0, 0, 0}); for(auto& x : a) {cin >> x.u >> x.v >> x.c; x.u--; x.v--;}
vvl to_edge(const ll n, const vector<uv>& v) { vvl ret(n); for (auto& x : v) ret[x.u].push_back(x.v); return ret; }
vvl to_edge_d(const ll n, const vector<uv>& v) { vvl ret(n); for (auto& x : v) { ret[x.u].push_back(x.v); ret[x.v].push_back(x.u); } return ret; }

template <class T = long long> using pql = priority_queue<T>;
template <class T = long long> using pqg = priority_queue<T, vector<T>, greater<T>>;
using vm = vector<mint>; using vvm = vector<vm>;

ostream& operator<<(ostream& os, const mint& v) { os << v.val(); return os; }
void yn(bool f) { std::cout << (f ? "Yes" : "No") << endl; };
template<class T> void ov(const T& v) { for (auto it = v.begin(); it != v.end(); it++) { if (it != v.begin()) cout << " "; cout << *it; } };
template<> void ov(const vm& v) { for (auto it = v.begin(); it != v.end(); it++) { if (it != v.begin()) cout << " "; cout << it->val(); } };

const ll llhuge = 1LL << 62; //十分でかいが多少足しても溢れない数値
auto gmax(const auto& a, const auto& b) { return a > b ? a : b; };
auto gmin(const auto& a, const auto& b) { return a < b ? a : b; };
bool chmin(auto& a, const auto& b) { const auto olda = a; a = gmin(a, b); return olda != a; }
bool chmax(auto& a, const auto& b) { const auto olda = a; a = gmax(a, b); return olda != a; }
void sort(auto& v) { std::ranges::sort(v); };
void rev(auto& v) { std::ranges::reverse(v); };
template<class T> auto p_sum(const T& v) { T ret(v.size()); std::partial_sum(begin(v), end(v), ret.begin()); return ret; };
template<class T, class K = T::key_type, class V = T::mapped_type> [[nodiscard]] V myat(const T& mp, const K& key) { return mp.find(key) == mp.end() ? V() : mp.at(key); }
long long ceil(const long long a, const long long b) { return (a + b - 1) / b; }

int main() {
	cin.tie(nullptr);
	ios::sync_with_stdio(false);

	ll h, w;
	cin >> h >> w;
	vvl a(h, vl(w));
	REPM(x, a) REPM(y, x) cin >> y;
	
	pqg<tuple<ll, ll, ll>> pq1;
	pqg<tuple<ll, ll, ll>> pq2;

	pq1.push({ 0, 0, 0 });
	pq2.push({ 0, h-1, w-1 });

	ll ans = -2;
	bool flg = true;
	while (flg) {
		{
			++ans;
			while (a[get<1>(pq1.top())][get<2>(pq1.top())] == -1) pq1.pop();
			auto [c1, x1, y1] = pq1.top();
			pq1.pop();
			a[x1][y1] = -1;

			REP(i, 4) {
				ll nx = (i == 0) ? x1 - 1 : (i == 1) ? x1 + 1 : x1;
				ll ny = (i == 2) ? y1 - 1 : (i == 3) ? y1 + 1 : y1;
				if (nx < 0 || nx >= h || ny < 0 || ny >= w) continue;
				if (a[nx][ny] == -1) continue;
				else if (a[nx][ny] == -2) flg = false;
				else {
					pq1.push({ a[nx][ny], nx, ny });
				}
			}
		}
		if (!flg) break;

		{
			++ans;
			while (a[get<1>(pq2.top())][get<2>(pq2.top())] == -2) pq2.pop();
			auto [c1, x1, y1] = pq2.top();
			a[x1][y1] = -2;
			pq2.pop();

			REP(i, 4) {
				ll nx = (i == 0) ? x1 - 1 : (i == 1) ? x1 + 1 : x1;
				ll ny = (i == 2) ? y1 - 1 : (i == 3) ? y1 + 1 : y1;
				if (nx < 0 || nx >= h || ny < 0 || ny >= w) continue;
				if (a[nx][ny] == -2) continue;
				else if (a[nx][ny] == -1) flg = false;
				else {
					pq2.push({ a[nx][ny], nx, ny });
				}
			}
			if (!flg) break;
		}

	}

	cout << ans << endl;

}