Buggy python submission (verdict: Runtime Error):
H, W = map(int, input().split())
S = [input() for _ in range(H)]
M = [[float('inf') for _ in range(W)] for _ in range(H)]


def dfs(x, y, c):
    cc = float('inf')
    for xx, yy in [(x + 1, y), (x, y + 1), (x - 1, y), (x, y - 1)]:
        if (H, W) == (yy + 1, xx + 1):
            return c + 1
        if 0 <= yy < H and 0 <= xx < W and S[yy][xx] == '.' and \
                (M[yy][xx] > c + 1):
            M[yy][xx] = c + 1
            cc = min(cc, dfs(xx, yy, c + 1))
    return cc


def main():
    ans = 0
    for i in range(H):
        ans += S[i].count('.')
    c = dfs(0, 0, 1)
    if c == float('inf'):
        print(-1)
    else:
        print(ans - c)


main()


Fixed submission:
H, W = map(int, input().split())
S = [input() for _ in range(H)]


def bfs():
    q = [(0, 0)]
    nq = []
    m = []
    c = 1
    while len(q) > 0:
        while len(q) > 0:
            x, y = q.pop(0)
            for xx, yy in [(x + 1, y), (x, y + 1), (x - 1, y), (x, y - 1)]:
                if (H, W) == (yy + 1, xx + 1):
                    return c + 1
                if 0 <= yy < H and 0 <= xx < W and S[yy][xx] == '.' and \
                        (xx, yy) not in m:
                    m.append((xx, yy))
                    nq.append((xx, yy))
        q = nq
        nq = []
        c += 1
    return -1


def main():
    ans = 0
    for i in range(H):
        ans += S[i].count('.')
    c = bfs()
    if c == -1:
        print(-1)
    else:
        print(ans - c)


main()

Buggy python submission (verdict: Runtime Error):
H, W = map(int, input().split())
S = [input() for _ in range(H)]
M = {(0, 0): 1}


def dfs(x, y, c):
    cc = float('inf')
    for xx, yy in [(x + 1, y), (x, y + 1), (x - 1, y), (x, y - 1)]:
        if (H, W) == (yy + 1, xx + 1):
            return c + 1
        if 0 <= yy < H and 0 <= xx < W and S[yy][xx] == '.' and \
                ((xx, yy) not in M or M[(xx, yy)] > c + 1):
            M[(xx, yy)] = c + 1
            cc = min(cc, dfs(xx, yy, c + 1))
    return cc


def main():
    dfs(0, 0, 1)
    # ans = 0
    # for i in range(H):
    #     ans += S[i].count('.')
    # c = dfs(0, 0, 1)
    # if c == float('inf'):
    #     print(-1)
    # else:
    #     print(ans - c)


main()


Fixed submission:
H, W = map(int, input().split())
S = [input() for _ in range(H)]


def bfs():
    q = [(0, 0)]
    nq = []
    m = []
    c = 1
    while len(q) > 0:
        while len(q) > 0:
            x, y = q.pop(0)
            for xx, yy in [(x + 1, y), (x, y + 1), (x - 1, y), (x, y - 1)]:
                if (H, W) == (yy + 1, xx + 1):
                    return c + 1
                if 0 <= yy < H and 0 <= xx < W and S[yy][xx] == '.' and \
                        (xx, yy) not in m:
                    m.append((xx, yy))
                    nq.append((xx, yy))
        q = nq
        nq = []
        c += 1
    return -1


def main():
    ans = 0
    for i in range(H):
        ans += S[i].count('.')
    c = bfs()
    if c == -1:
        print(-1)
    else:
        print(ans - c)


main()

Buggy python submission (verdict: Runtime Error):
H, W = map(int, input().split())
S = [input() for _ in range(H)]
M = {(0, 0): 1}


def dfs(x, y, c):
    cc = float('inf')
    for xx, yy in [(x + 1, y), (x, y + 1), (x - 1, y), (x, y - 1)]:
        if (H, W) == (yy + 1, xx + 1):
            return c + 1
        if 0 <= yy < H and 0 <= xx < W and S[yy][xx] == '.' and \
                ((xx, yy) not in M or M[(xx, yy)] > c + 1):
            M[(xx, yy)] = c + 1
            cc = min(cc, dfs(xx, yy, c + 1))
    return cc


def main():
    ans = 0
    for i in range(H):
        ans += S[i].count('.')
    c = dfs(0, 0, 1)
    if c == float('inf'):
        print(-1)
    else:
        print(ans - c)


main()


Fixed submission:
H, W = map(int, input().split())
S = [input() for _ in range(H)]


def bfs():
    q = [(0, 0)]
    nq = []
    m = []
    c = 1
    while len(q) > 0:
        while len(q) > 0:
            x, y = q.pop(0)
            for xx, yy in [(x + 1, y), (x, y + 1), (x - 1, y), (x, y - 1)]:
                if (H, W) == (yy + 1, xx + 1):
                    return c + 1
                if 0 <= yy < H and 0 <= xx < W and S[yy][xx] == '.' and \
                        (xx, yy) not in m:
                    m.append((xx, yy))
                    nq.append((xx, yy))
        q = nq
        nq = []
        c += 1
    return -1


def main():
    ans = 0
    for i in range(H):
        ans += S[i].count('.')
    c = bfs()
    if c == -1:
        print(-1)
    else:
        print(ans - c)


main()

Buggy python submission (verdict: Runtime Error):
H, W = map(int, input().split())
S = [input() for _ in range(H)]
M = [(0, 0)]


def dfs(x, y, c):
    cc = float('inf')
    for xx, yy in [(x + 1, y), (x, y + 1), (x - 1, y), (x, y - 1)]:
        if (H, W) == (yy + 1, xx + 1):
            return c + 1
        if 0 <= yy < H and 0 <= xx < W and S[yy][xx] == '.' and \
                (xx, yy) not in M:
            M.append((xx, yy))
            cc = min(cc, dfs(xx, yy, c + 1))
    return cc


def main():
    ans = 0
    for i in range(H):
        ans += S[i].count('.')
    c = dfs(0, 0, 1)
    if c == float('inf'):
        print(-1)
    else:
        print(ans - c)


main()


Fixed submission:
H, W = map(int, input().split())
S = [input() for _ in range(H)]


def bfs():
    q = [(0, 0)]
    nq = []
    m = []
    c = 1
    while len(q) > 0:
        while len(q) > 0:
            x, y = q.pop(0)
            for xx, yy in [(x + 1, y), (x, y + 1), (x - 1, y), (x, y - 1)]:
                if (H, W) == (yy + 1, xx + 1):
                    return c + 1
                if 0 <= yy < H and 0 <= xx < W and S[yy][xx] == '.' and \
                        (xx, yy) not in m:
                    m.append((xx, yy))
                    nq.append((xx, yy))
        q = nq
        nq = []
        c += 1
    return -1


def main():
    ans = 0
    for i in range(H):
        ans += S[i].count('.')
    c = bfs()
    if c == -1:
        print(-1)
    else:
        print(ans - c)


main()

Buggy python submission (verdict: Runtime Error):
import math


H, W = map(int, input().split())
S = [input() for _ in range(H)]
M = [(0, 0)]


def dfs(x, y, c):
    cc = float('inf')
    for xx, yy in [(x + 1, y), (x, y + 1), (x - 1, y), (x, y - 1)]:
        if (H, W) == (yy + 1, xx + 1):
            return c + 1
        if 0 <= yy < H and 0 <= xx < W and S[yy][xx] == '.' and \
                (xx, yy) not in M:
            M.append((xx, yy))
            cc = min(cc, dfs(xx, yy, c + 1))
    return cc


def main():
    ans = 0
    for i in range(H):
        ans += S[i].count('.')
    c = dfs(0, 0, 1)
    if c == math.inf:
        print(-1)
    else:
        print(ans - c)


main()


Fixed submission:
H, W = map(int, input().split())
S = [input() for _ in range(H)]


def bfs():
    q = [(0, 0)]
    nq = []
    m = []
    c = 1
    while len(q) > 0:
        while len(q) > 0:
            x, y = q.pop(0)
            for xx, yy in [(x + 1, y), (x, y + 1), (x - 1, y), (x, y - 1)]:
                if (H, W) == (yy + 1, xx + 1):
                    return c + 1
                if 0 <= yy < H and 0 <= xx < W and S[yy][xx] == '.' and \
                        (xx, yy) not in m:
                    m.append((xx, yy))
                    nq.append((xx, yy))
        q = nq
        nq = []
        c += 1
    return -1


def main():
    ans = 0
    for i in range(H):
        ans += S[i].count('.')
    c = bfs()
    if c == -1:
        print(-1)
    else:
        print(ans - c)


main()

Buggy python submission (verdict: Runtime Error):
H, W = map(int, input().split())
S = [input() for _ in range(H)]
M = [(0, 0)]


def dfs(x, y, c):
    cc = float('inf')
    for xx, yy in [(x + 1, y), (x, y + 1), (x - 1, y), (x, y - 1)]:
        if (H, W) == (yy + 1, xx + 1):
            return c + 1
        if 0 <= yy < H and 0 <= xx < W and S[yy][xx] == '.' and \
                (xx, yy) not in M:
            M.append((xx, yy))
            cc = min(cc, dfs(xx, yy, c + 1))
    return cc


def main():
    ans = 0
    for i in range(H):
        ans += S[i].count('.')
    print(ans - dfs(0, 0, 1))


main()


Fixed submission:
H, W = map(int, input().split())
S = [input() for _ in range(H)]


def bfs():
    q = [(0, 0)]
    nq = []
    m = []
    c = 1
    while len(q) > 0:
        while len(q) > 0:
            x, y = q.pop(0)
            for xx, yy in [(x + 1, y), (x, y + 1), (x - 1, y), (x, y - 1)]:
                if (H, W) == (yy + 1, xx + 1):
                    return c + 1
                if 0 <= yy < H and 0 <= xx < W and S[yy][xx] == '.' and \
                        (xx, yy) not in m:
                    m.append((xx, yy))
                    nq.append((xx, yy))
        q = nq
        nq = []
        c += 1
    return -1


def main():
    ans = 0
    for i in range(H):
        ans += S[i].count('.')
    c = bfs()
    if c == -1:
        print(-1)
    else:
        print(ans - c)


main()