Buggy python submission (verdict: Time Limit Exceeded):
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.readline
readlines = sys.stdin.buffer.readlines
sys.setrecursionlimit(10 ** 7)

h, w = map(int, readline().split())
grid = [[0]*(w) for _ in range(h)]

black = []
for i in range(h):
    for j, k in enumerate(readline()):
        if k == "#":
            black.append((i, j))
            grid[i][j] = 1

ans = 0
d = ((0, 1),
     (1, 0),
     (0, -1),
     (-1, 0),)
while True:
    paint = []
    while black:
        x, y = black.pop()
        for nx, ny in d:
            if x+nx == -1 or x+nx == h or y+ny == -1 or y+ny == w:
                continue
            if not grid[nx + x][ny + y]:
                grid[nx + x][ny + y] = 1
                paint.append((nx + x, ny + y))

    if len(paint) == 0:
        break
    black = paint[:]
    ans += 1

print(ans)


Fixed submission:
h, w = map(int, input().split())
grid = [[0]*(w+2) for _ in range(h+2)]

black = []
for i in range(h):
    for j, k in enumerate(input()):
        if k == "#":
            black.append((i + 1, j + 1))
            grid[i+1][j+1] = 1

ans = 0
d = ((0, 1),
     (1, 0),
     (0, -1),
     (-1, 0),)
while True:
    paint = []
    while black:
        x, y = black.pop()
        if x == 0 or x == h + 1 or y == 0 or y == w + 1:
            continue
        else:
            for nx, ny in d:
                if not grid[nx + x][ny + y]:
                    if x+nx == 0 or x+nx == h + 1 or y+ny == 0 or y+ny == w + 1:
                        continue
                    grid[nx + x][ny + y] = 1
                    paint.append((nx + x, ny + y))

    if len(paint) == 0:
        break
    black = paint[:]
    ans += 1

print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
h, w = map(int, input().split())
grid = [[0]*(w) for _ in range(h)]

black = []
for i in range(h):
    for j, k in enumerate(input()):
        if k == "#":
            black.append((i, j))
            grid[i][j] = 1

ans = 0
d = ((0, 1),
     (1, 0),
     (0, -1),
     (-1, 0),)
while True:
    paint = []
    while black:
        x, y = black.pop()
        for nx, ny in d:
            if x+nx == -1 or x+nx == h or y+ny == -1 or y+ny == w:
                continue
            if not grid[nx + x][ny + y]:
                grid[nx + x][ny + y] = 1
                paint.append((nx + x, ny + y))

    if len(paint) == 0:
        break
    black = paint[:]
    ans += 1

print(ans)

Fixed submission:
h, w = map(int, input().split())
grid = [[0]*(w+2) for _ in range(h+2)]

black = []
for i in range(h):
    for j, k in enumerate(input()):
        if k == "#":
            black.append((i + 1, j + 1))
            grid[i+1][j+1] = 1

ans = 0
d = ((0, 1),
     (1, 0),
     (0, -1),
     (-1, 0),)
while True:
    paint = []
    while black:
        x, y = black.pop()
        if x == 0 or x == h + 1 or y == 0 or y == w + 1:
            continue
        else:
            for nx, ny in d:
                if not grid[nx + x][ny + y]:
                    if x+nx == 0 or x+nx == h + 1 or y+ny == 0 or y+ny == w + 1:
                        continue
                    grid[nx + x][ny + y] = 1
                    paint.append((nx + x, ny + y))

    if len(paint) == 0:
        break
    black = paint[:]
    ans += 1

print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
h, w = map(int, input().split())
grid = [[0]*(w+2) for _ in range(h+2)]

black = []
for i in range(h):
    for j, k in enumerate(input()):
        if k == "#":
            black.append((i + 1, j + 1))
            grid[i+1][j+1] = 1

ans = 0
d = ((0, 1),
     (1, 0),
     (0, -1),
     (-1, 0),)
while True:
    paint = []
    while black:
        x, y = black.pop()
        if x == 0 or x == h + 1 or y == 0 or y == w + 1:
            continue
        else:
            for nx, ny in d:
                if not grid[nx + x][ny + y]:
                    if x+nx == 0 or x+nx == h + 1 or y+ny == 0 or y+ny == w + 1:
                        continue
                    grid[nx + x][ny + y] = 1
                    paint.append((nx + x, ny + y))

    if len(paint) == 0:
        break
    black = paint[:]
    ans += 1

print(ans)


Fixed submission:
h, w = map(int, input().split())
grid = [[0]*(w+2) for _ in range(h+2)]

black = []
for i in range(h):
    for j, k in enumerate(input()):
        if k == "#":
            black.append((i + 1, j + 1))
            grid[i+1][j+1] = 1

ans = 0
d = ((0, 1),
     (1, 0),
     (0, -1),
     (-1, 0),)
while True:
    paint = []
    while black:
        x, y = black.pop()
        if x == 0 or x == h + 1 or y == 0 or y == w + 1:
            continue
        else:
            for nx, ny in d:
                if not grid[nx + x][ny + y]:
                    if x+nx == 0 or x+nx == h + 1 or y+ny == 0 or y+ny == w + 1:
                        continue
                    grid[nx + x][ny + y] = 1
                    paint.append((nx + x, ny + y))

    if len(paint) == 0:
        break
    black = paint[:]
    ans += 1

print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
import numpy as np
h, w = map(int, input().split())
grid = np.zeros((h + 2, w + 2), dtype=int)

black = []
for i in range(h):
    for j, k in enumerate(input()):
        if k == "#":
            black.append((i + 1, j + 1))
            grid[i+1][j+1] = True

ans = 0
d = ((0, 1),
     (1, 0),
     (0, -1),
     (-1, 0),)
while not grid[1: h + 1, 1: w + 1].all():
    paint = []
    while black:
        x, y = black.pop()
        if x == 0 or x == h + 1 or y == 0 or y == w + 1:
            continue
        else:
            for nx, ny in d:
                if not grid[nx + x][ny + y]:
                    grid[nx + x][ny + y] = 1
                    paint.append((nx + x, ny + y))

    black = paint[:]
    ans += 1

print(ans)


Fixed submission:
h, w = map(int, input().split())
grid = [[0]*(w+2) for _ in range(h+2)]

black = []
for i in range(h):
    for j, k in enumerate(input()):
        if k == "#":
            black.append((i + 1, j + 1))
            grid[i+1][j+1] = 1

ans = 0
d = ((0, 1),
     (1, 0),
     (0, -1),
     (-1, 0),)
while True:
    paint = []
    while black:
        x, y = black.pop()
        if x == 0 or x == h + 1 or y == 0 or y == w + 1:
            continue
        else:
            for nx, ny in d:
                if not grid[nx + x][ny + y]:
                    if x+nx == 0 or x+nx == h + 1 or y+ny == 0 or y+ny == w + 1:
                        continue
                    grid[nx + x][ny + y] = 1
                    paint.append((nx + x, ny + y))

    if len(paint) == 0:
        break
    black = paint[:]
    ans += 1

print(ans)