import collections,sys,math,functools,operator,itertools,bisect,heapq,decimal,string,time,random
#sys.setrecursionlimit(10**9)
#sys.set_int_max_str_digits(0)
#input = sys.stdin.readline
#n = int(input())
#
#alist = []
#s = input()
h,w = map(int,input().split())
grid = [list(map(int,input().split())) for i in range(h)]
color = [[],[]]
s = [set(),set()]
c = [[-1 for i in range(w)] for j in range(h)]
c[0][0] = 0
c[h-1][w-1] = 1
heapq.heappush(color[0],(grid[0][1],0,1))
heapq.heappush(color[0],(grid[1][0],1,0))
s[0].add((0,1))
s[0].add((1,0))
s[0].add((0,0))
heapq.heappush(color[1],(grid[h-2][w-1],h-2,w-1))
heapq.heappush(color[1],(grid[h-1][w-2],h-1,w-2))
s[1].add((h-2,w-1))
s[1].add((h-1,w-2))
s[1].add((h-1,w-1))
ans = 0
dxy = [[-1,0],[1,0],[0,1],[0,-1]]
for i in range(h*w):
    v,x,y = heapq.heappop(color[i%2])
    while c[x][y] != -1:
        if not color[i%2]:
            print(ans)
            exit()
        v,x,y = heapq.heappop(color[i%2])
    c[x][y] = i%2
    ans += 1
    for dx,dy in dxy:
        if 0 <= x+dx < h and 0 <= y+dy < w:
            if c[x+dx][y+dy] == (i%2)^1:
                exit(print(ans))
            if (x+dx,y+dy) not in s[i%2]:
                s[i%2].add((x+dx,y+dy))
                heapq.heappush(color[i%2],(grid[x+dx][y+dy],x+dx,y+dy))