from heapq import heappop, heappush

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

# くっつくまでやる
a_q = [(a[0][0], 0, 0)]
b_q = [(a[-1][-1], h - 1, w - 1)]

colors = [[-1] * w for _ in range(h)]

go = True
turn = 0
cnt = 0
DXDY = [(1, 0), (0, 1), (-1, 0), (0, -1)]

while go:
    # print(a_q, b_q, turn)

    if turn == 0:
        _, y, x = heappop(a_q)
    else:
        _, y, x = heappop(b_q)

    if colors[y][x] != -1:
        continue

    colors[y][x] = turn
    for dx, dy in DXDY:
        nx, ny = x + dx, y + dy
        if 0 <= nx < w and 0 <= ny < h:
            if colors[ny][nx] == -1:
                if turn == 0:
                    heappush(a_q, (a[ny][nx], ny, nx))
                else:
                    heappush(b_q, (a[ny][nx], ny, nx))
            elif colors[ny][nx] != turn:
                go = False

    turn = 1 - turn
    cnt += 1

print(cnt - 2)