import typing
import sys
from collections import defaultdict
import heapq
input = lambda: sys.stdin.readline().strip()
inf = 10**18
mod = 998244353
# import pypyjit
# pypyjit.set_param('max_unroll_recursion=-1')
# sys.setrecursionlimit(10**6)

def solve():
  H, W = map(int, input().split())
  grid = []
  for _ in range(H):
    grid.append(list(map(int, input().split())))
  color = [[-1]*W for _ in range(H)]
  q = [[(grid[-1][-1], H-1, W-1)], [(grid[0][0], 0, 0)]]
  cnt = -2
  while True:
    while True:
      _, h, w = heapq.heappop(q[(cnt-1)%2])
      if color[h][w] == -1:
        break
    cnt += 1
    color[h][w] = cnt%2
    # 隣あっているマスに異なるいろがあったら終わり
    for dh, dw in zip([1, 0, -1, 0], [0, 1, 0, -1]):
      if 0 <= dh + h <= H-1 and 0 <= dw + w <= W-1:
        if color[dh + h][dw + w]==-1:
          heapq.heappush(q[cnt%2], (grid[dh+h][dw+w], dh+h, dw+w))
        if color[dh + h][dw + w]==(cnt-1)%2:
          print(cnt)
          return
      

  


def main():
  t = 1
  for _ in range(t):
    solve()
main()