module main;
// https://mmxsrup.hatenablog.com/entry/2016/09/20/235927 より
// 2次元グリッド、幅優先探索
import std;

// 多次元配列をある値で埋める
void fill(A, T)(ref A a, T value) if (isArray!A)
{
	alias E = ElementType!A;
	static if (isArray!E) {
		foreach (ref e; a)
			fill(e, value);
	} else {
		a[] = value;
	}
}
// C++ の tie
auto tie(StoreElements...)(ref StoreElements stores)
{
	alias Elements = staticMap!(Unqual, StoreElements);
	
	template toPointer(T)
	{
		alias toPointer = T*;
	}
	
	struct Holder
	{
		alias StoreElementsPtrs = staticMap!(toPointer, StoreElements);
		StoreElementsPtrs storePtrs;
		
		this(ref StoreElements stores)
		{
			foreach(i, _; StoreElements)
			{
				storePtrs[i] = &stores[i];
			}
		}
		
		void opAssign(Tuple!Elements values)
		{
			foreach(i, _; Elements)
			{
				*storePtrs[i] = values[i];
			}
		}
	}
	
	return Holder(stores);
}
struct Point {
	int y, x;
	Point opBinary(string op)(Point rhs) const
		if (op == "+")
	{
		return Point(y + rhs.y, x + rhs.x);
	}
}
// 上 右 下 左 0 1 2 3
auto dir = [
	Point(1, 0),
	Point(0, 1),
	Point(-1, 0),
	Point(0, -1)
];
void main()
{
	// 入力
	int W, H;
	readln.chomp.formattedRead("%d %d", W, H);
	auto M = new int[][](H);
	foreach (ref row; M)
		row = readln.split.to!(int[]);
	// 答えの計算
	immutable INF = 10 ^^ 9;
	auto dist = uninitializedArray!(int[][][])(H, W, 4);
	fill(dist, INF);
	alias T = Tuple!(Point, Point, int);
	auto que = DList!T(T(Point(0, 1), Point(0, 0), 1), T(Point(1, 0), Point(0, 0), 2));
	dist[0][0][] = 0;
	dist[0][1][1] = 1;
	dist[1][0][2] = 1;

	while (!que.empty) {
		Point p1, p2;	// 1つ前、2つ前
		int v;	// どの方向から来たか
		tie(p1, p2, v) = que.front;
		que.removeFront;
		if (p1.y == H - 1 && p1.x == W - 1) break;

		foreach (i; 0 .. 4) {
			Point nxt = p1 + dir[i];
			if (nxt.y < 0 || nxt.y >= H || nxt.x < 0 || nxt.x >= W) continue;
			if (dist[nxt.y][nxt.x][i] != INF) continue;

			int len0 = M[nxt.y][nxt.x];
			int len1 = M[p1.y][p1.x];
			int len2 = M[p2.y][p2.x];
			if (len0 == len1 || len1 == len2 || len2 == len0) continue;
			int mid = len0 + len1 + len2 - min(len0, len1, len2) - max(len0, len1, len2);
			if (mid == len0 || mid == len2) {
				que.insertBack(T(nxt, p1, i));
				dist[nxt.y][nxt.x][i] = dist[p1.y][p1.x][v] + 1; 
			}
		}
	}
	// 答えの出力
	int ans = dist[H - 1][W - 1].minElement;
	writeln(ans == INF ? -1 : ans);
}