from heapq import *

# 入力
h,w = map(int,input().split())
A = [list(map(int,input().split())) for _ in range(h)]

# BFSで使うqueを用意
queA = [(A[0][0], 0, 0)]
heapify(queA)
colorA = [[-1 for j in range(w)]for i in range(h)]
usedA = [[-1 for j in range(w)]for i in range(h)]
usedA[0][0] = 0

queB = [(A[-1][-1], h-1, w-1)]
heapify(queB)
colorB = [[-1 for j in range(w)]for i in range(h)]
usedB = [[-1 for j in range(w)]for i in range(h)]
usedB[-1][-1] = 1

# マス(i,j)と隣接している頂点リストを返す
def nextV(i,j):
    V = []
    # 上
    if((i == 0) == False):
        V.append((A[i-1][j], i-1, j))
    # 下
    if((i == h-1) == False):
        V.append((A[i+1][j], i+1, j))
    # 左
    if((j == 0) == False):
        V.append((A[i][j-1], i, j-1))
    # 右
    if((j == w-1) == False):
        V.append((A[i][j+1], i, j+1))
        
    return V

# 色1を広げる
def f():
    v = heappop(queA)
    colorA[v[1]][v[2]] = 1
    # 色1と色0が隣接したら出力
    for nv in nextV(v[1], v[2]):
        if(colorB[nv[1]][nv[2]] == 0):
            print(i-1)
            exit()
    
    # 次の頂点をみる
    for nv in nextV(v[1], v[2]):
        if(usedA[nv[1]][nv[2]] == -1):
            heappush(queA, nv)
            usedA[nv[1]][nv[2]] = 0

# 色0を広げる        
def g():
    v = heappop(queB)
    colorB[v[1]][v[2]] = 0
    # 色1と色0が隣接したら出力
    for nv in nextV(v[1], v[2]):
        if(colorA[nv[1]][nv[2]] == 1):
            print(i-1)
            exit()
    
    # 次の頂点をみる
    for nv in nextV(v[1], v[2]):
        if(usedB[nv[1]][nv[2]] == -1):
            heappush(queB, nv)
            usedB[nv[1]][nv[2]] = 0

# 愚直にシミュレーション
for i in range(h*w):
    if(i%2 == 0):
        f()
    elif(i%2 == 1):
        g()