from heapq import *
H, W = map(int, input().split())
A = [list(map(int, input().split())) for _ in range(H)]
assert(len(set([A[i][j] for i in range(H) for j in range(W)])) == H * W)
q = [[], []]
C = [[-1] * W for _ in range(H)]
B = [[False] * W for _ in range(H)]
heappush(q[1], (A[0][0], 0, 0, 1))
heappush(q[0], (A[H - 1][W - 1], H - 1, W - 1, 0))
for k in range(1, H * W + 1):
	_, i, j, c = heappop(q[k % 2])
	C[i][j] = c
	B[i][j] = True
	for dx, dy in [(-1, 0), (0, -1), (1, 0), (0, 1)]:
		x = i + dx
		y = j + dy
		if 0 <= x < H and 0 <= y < W:
			if C[x][y] == -1 and not B[x][y]:
				heappush(q[k % 2], (A[x][y], x, y, c))
				B[x][y] = True
			elif C[x][y] != C[i][j]:
				exit(print(k - 2))