from heapq import heappop, heappush

DIJ = [(-1, 0), (0, -1), (0, 1), (1, 0)]

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

color = [[-1]*W for _ in range(H)]
que = [[(A[-1][-1], H-1, W-1)], [(A[0][0], 0, 0)]]

for t in range(-1, H*W-1):
  while True:
    a, i, j = heappop(que[t%2])
    if color[i][j] == -1: break
  color[i][j] = t%2
  for ni, nj in DIJ:
    ni += i; nj += j
    if not H > ni >= 0 <= nj < W: continue
    if color[ni][nj] == -1:
      heappush(que[t%2], (A[ni][nj], ni, nj))
    elif color[ni][nj] != t%2: break
  else: continue
  print(t); break