import heapq


H, W = map(int, input().split())
A = [list(map(int, input().split())) for _ in range(H)]

if H == W == 2:
	print(0)
	exit()

visit = [[-1] * W for _ in range(H)]
visit[0][0] = 1
visit[-1][-1] = 0
n = [[(A[H-1][W-2], H-1, W-2), (A[H-2][W-1], H-2, W-1)], [(A[0][1], 0, 1), (A[1][0], 1, 0)]]
s = [set([(H-1, W-2), (H-2, W-1)]), set([(0, 1), (1, 0)])]
heapq.heapify(n[0])
heapq.heapify(n[1])

idx = 1
while 1:
	if not n[idx%2]:
		break
	mi = heapq.heappop(n[idx%2])
	while visit[mi[1]][mi[2]] != -1 and n[idx%2]:
		mi = heapq.heappop(n[idx%2])
	if visit[mi[1]][mi[2]] != -1:
		break

	visit[mi[1]][mi[2]] = idx % 2
	fin = False
	for i, j in [(0, 1), (0, -1), (1, 0), (-1, 0)]:
		if 0 <= mi[1] + i < H and 0 <= mi[2] + j < W and visit[mi[1]+i][mi[2]+j] == (idx+1) % 2:
			fin = True
			break
		if 0 <= mi[1] + i < H and 0 <= mi[2] + j < W and visit[mi[1]+i][mi[2]+j] == -1 and (mi[1]+i, mi[2]+j) not in s[idx%2]:
			heapq.heappush(n[idx%2], (A[mi[1]+i][mi[2]+j], mi[1]+i, mi[2]+j))
			s[idx%2].add((mi[1]+i, mi[2]+j))
	if fin:
		break

	idx += 1
print(idx)