Buggy python submission (verdict: Runtime Error):
import sys
import numpy as np
from heapq import heappop, heappush

# Dijikstra
def main():
    H, W = map(int, sys.stdin.readline().split())

    grid = np.array([list(sys.stdin.readline().rstrip()) for _ in range(H)])
    grid = np.pad(grid, 1)
    # atcoderではnp.pad() のargにconstant_valuesを指定できない
    q = []
    heappush(q, (0, 1, 1))
    visited = set()
    cost = np.full((H + 1, W + 1), np.inf)
    cost[1][1] = 0
    while q:
        c, i, j = heappop(q)
        if (i, j) in visited:
            continue
        visited.add((i, j))
        cost[i][j] = c
        if i == H and j == W:
            break
        for dy, dx in [(1, 0), (0, 1), (-1, 0), (0, -1)]:
            y = i + dy
            x = j + dx
            if grid[y][x] == '.' and not (y, x) in visited:
                heappush(q, (c + 1, y, x))
    

    if cost[H][W] != np.inf:
        ans = int(np.sum(grid == '.') - (cost[H][W] + 1))
    else:
        ans = -1

    print(ans)  
if __name__ == "__main__":
    main()

Fixed submission:
import sys
import numpy as np
from heapq import heappop, heappush


def main():
    H, W = map(int, sys.stdin.readline().split())

    grid = np.array([list(sys.stdin.readline().rstrip()) for _ in range(H)], dtype='U')
    grid = np.pad(grid, 1, mode='constant')

    can_go = False
    i = j = 1 # start
    c = 0     # real cost
    h = max(H - i, W - j) # goalまでの推定cost 
    s = c + h # score
    q = [] # open list
    heappush(q, (s, c, i, j))
    visited = set() # closed list
    # parent = [[None * (W + 1)] for _ in range(H+1)]

    while q:
        s, c, i, j = heappop(q)
        visited.add((i, j))
        if c == s: 
            can_go = True
            break
        for dy, dx in [(1, 0), (0, 1), (-1, 0), (0, -1)]:
            y = i + dy
            x = j + dx
            if grid[y][x] == '.' and not (y, x) in visited:
                visited.add((y, x))
                h = max(H - y, W - x)
                s = h + c + 1
                heappush(q, (s, c+1, y, x))
 
    if can_go:
        ans = (grid == '.').sum() - (c + 1)
    else:
        ans = -1
    print(ans)


if __name__ == "__main__":
    main()

Buggy python submission (verdict: Runtime Error):
import sys
import numpy as np
from heapq import heappop, heappush


def main():
    H, W = map(int, sys.stdin.readline().split())

    grid = np.array([list(sys.stdin.readline().rstrip()) for _ in range(H)], dtype='U')
    grid = np.pad(grid, 1, mode='constant',constant_values='#')

    can_go = False
    i = j = 1 # start
    c = 0     # real cost
    h = max(H - i, W - j) # goalまでの推定cost 
    s = c + h # score
    q = [] # open list
    heappush(q, (s, c, i, j))
    visited = set() # closed list
    # parent = [[None * (W + 1)] for _ in range(H+1)]

    while q:
        s, c, i, j = heappop(q)
        visited.add((i, j))
        if c == s: 
            can_go = True
            break
        for dy, dx in [(1, 0), (0, 1), (-1, 0), (0, -1)]:
            y = i + dy
            x = j + dx
            if grid[y][x] == '.' and not (y, x) in visited:
                visited.add((y, x))
                h = max(H - y, W - x)
                s = h + c + 1
                heappush(q, (s, c+1, y, x))
 
    if can_go:
        ans = (grid == '.').sum() - (c + 1)
    else:
        ans = -1
    print(ans)


if __name__ == "__main__":
    main()

Fixed submission:
import sys
import numpy as np
from heapq import heappop, heappush


def main():
    H, W = map(int, sys.stdin.readline().split())

    grid = np.array([list(sys.stdin.readline().rstrip()) for _ in range(H)], dtype='U')
    grid = np.pad(grid, 1, mode='constant')

    can_go = False
    i = j = 1 # start
    c = 0     # real cost
    h = max(H - i, W - j) # goalまでの推定cost 
    s = c + h # score
    q = [] # open list
    heappush(q, (s, c, i, j))
    visited = set() # closed list
    # parent = [[None * (W + 1)] for _ in range(H+1)]

    while q:
        s, c, i, j = heappop(q)
        visited.add((i, j))
        if c == s: 
            can_go = True
            break
        for dy, dx in [(1, 0), (0, 1), (-1, 0), (0, -1)]:
            y = i + dy
            x = j + dx
            if grid[y][x] == '.' and not (y, x) in visited:
                visited.add((y, x))
                h = max(H - y, W - x)
                s = h + c + 1
                heappush(q, (s, c+1, y, x))
 
    if can_go:
        ans = (grid == '.').sum() - (c + 1)
    else:
        ans = -1
    print(ans)


if __name__ == "__main__":
    main()

Buggy python submission (verdict: Runtime Error):
import sys
import numpy as np
from heapq import heappop, heappush


def main():
    H, W = map(int, sys.stdin.readline().split())

    grid = np.array([list(sys.stdin.readline().rstrip()) for _ in range(H)], dtype='U')
    grid = np.pad(grid, 1, constant_values=('#'))

    can_go = False
    i = j = 1 # start
    c = 0     # real cost
    h = max(H - i, W - j) # goalまでの推定cost 
    s = c + h # score
    q = [] # open list
    heappush(q, (s, c, i, j))
    visited = set() # closed list
    # parent = [[None * (W + 1)] for _ in range(H+1)]

    while q:
        s, c, i, j = heappop(q)
        visited.add((i, j))
        if c == s: 
            can_go = True
            break
        for dy, dx in [(1, 0), (0, 1), (-1, 0), (0, -1)]:
            y = i + dy
            x = j + dx
            if grid[y][x] == '.' and not (y, x) in visited:
                visited.add((y, x))
                h = max(H - y, W - x)
                s = h + c + 1
                heappush(q, (s, c+1, y, x))
 
    if can_go:
        ans = (grid == '.').sum() - (c + 1)
    else:
        ans = -1
    print(ans)


if __name__ == "__main__":
    main()

Fixed submission:
import sys
import numpy as np
from heapq import heappop, heappush


def main():
    H, W = map(int, sys.stdin.readline().split())

    grid = np.array([list(sys.stdin.readline().rstrip()) for _ in range(H)], dtype='U')
    grid = np.pad(grid, 1, mode='constant')

    can_go = False
    i = j = 1 # start
    c = 0     # real cost
    h = max(H - i, W - j) # goalまでの推定cost 
    s = c + h # score
    q = [] # open list
    heappush(q, (s, c, i, j))
    visited = set() # closed list
    # parent = [[None * (W + 1)] for _ in range(H+1)]

    while q:
        s, c, i, j = heappop(q)
        visited.add((i, j))
        if c == s: 
            can_go = True
            break
        for dy, dx in [(1, 0), (0, 1), (-1, 0), (0, -1)]:
            y = i + dy
            x = j + dx
            if grid[y][x] == '.' and not (y, x) in visited:
                visited.add((y, x))
                h = max(H - y, W - x)
                s = h + c + 1
                heappush(q, (s, c+1, y, x))
 
    if can_go:
        ans = (grid == '.').sum() - (c + 1)
    else:
        ans = -1
    print(ans)


if __name__ == "__main__":
    main()

Buggy python submission (verdict: Runtime Error):
import sys
import numpy as np
from heapq import heappop, heappush


def main():
    H, W = map(int, sys.stdin.readline().split())

    grid = np.array([list(sys.stdin.readline().rstrip()) for _ in range(H)])
    grid = np.pad(grid, 1, constant_values=('#'))

    can_go = False
    i = j = 1 # start
    c = 0     # real cost
    h = max(H - 1, W - 1) # goalまでの推定cost 
    s = c + h # score
    q = [] # open list
    heappush(q, (s, c, i, j))
    visited = set() # closed list
    # parent = [[None * (W + 1)] for _ in range(H+1)]

    while q:
        s, c, i, j = heappop(q)
        visited.add((i, j))
        if c == s:
            can_go = True
            break
        for dy, dx in [(1, 0), (0, 1), (-1, 0), (0, -1)]:
            y = i + dy
            x = j + dx
            if grid[y][x] == '.' and not (y, x) in visited:
                visited.add((y, x))
                h = max(H - y, W - x)
                s = h + c + 1
                heappush(q, (s, c+1, y, x))
 
    if can_go:
        ans = np.sum(grid == '.') - (c + 1)
    else:
        ans = -1
    print(ans)


if __name__ == "__main__":
    main()


Fixed submission:
import sys
import numpy as np
from heapq import heappop, heappush


def main():
    H, W = map(int, sys.stdin.readline().split())

    grid = np.array([list(sys.stdin.readline().rstrip()) for _ in range(H)], dtype='U')
    grid = np.pad(grid, 1, mode='constant')

    can_go = False
    i = j = 1 # start
    c = 0     # real cost
    h = max(H - i, W - j) # goalまでの推定cost 
    s = c + h # score
    q = [] # open list
    heappush(q, (s, c, i, j))
    visited = set() # closed list
    # parent = [[None * (W + 1)] for _ in range(H+1)]

    while q:
        s, c, i, j = heappop(q)
        visited.add((i, j))
        if c == s: 
            can_go = True
            break
        for dy, dx in [(1, 0), (0, 1), (-1, 0), (0, -1)]:
            y = i + dy
            x = j + dx
            if grid[y][x] == '.' and not (y, x) in visited:
                visited.add((y, x))
                h = max(H - y, W - x)
                s = h + c + 1
                heappush(q, (s, c+1, y, x))
 
    if can_go:
        ans = (grid == '.').sum() - (c + 1)
    else:
        ans = -1
    print(ans)


if __name__ == "__main__":
    main()