Buggy python submission (verdict: Time Limit Exceeded):
import sys
input=sys.stdin.readline

H, W = map(int, input().split())

a = []
for i in range(H):
    a.append(str(input()))

R = [[0] * W for i in range(H)]
L = [[0] * W for i in range(H)]
D = [[0] * W for i in range(H)]
U = [[0] * W for i in range(H)]

for i in range(H):
    cur = 0
    for j in range(W):
        if a[i][j] == "#":
            cur = 0
            U[i][j] = 0
        else:
            cur += 1
            if i == 0:
                U[i][j] = 1
            else:
                U[i][j] += U[i-1][j] + 1
        L[i][j] = cur

ans = 0
for i in reversed(range(H)):
    cur = 0
    for j in reversed(range(W)):
        if a[i][j] == "#":
            cur = 0
            D[i][j] = 0
        else:
            cur += 1
            if i == (H-1):
                D[i][j] = 1
            else:
                D[i][j] += D[i+1][j] + 1
        R[i][j] = cur
        if L[i][j] + R[i][j] + D[i][j] + U[i][j] -3 > ans:
            ans = L[i][j] + R[i][j] + D[i][j] + U[i][j] -3

print(ans)

Fixed submission:
import sys
input=sys.stdin.readline

H, W = map(int, input().split())

a = []
for i in range(H):
    a.append(str(input()))

R = [[0] * W for i in range(H)]
L = [[0] * W for i in range(H)]
D = [[0] * W for i in range(H)]
U = [[0] * W for i in range(H)]

for i in range(H):
    cur = 0
    for j in range(W):
        if a[i][j] == "#":
            cur = 0
            U[i][j] = 0
        else:
            cur += 1
            if i == 0:
                U[i][j] = 1
            else:
                U[i][j] += U[i-1][j] + 1
        L[i][j] = cur

ans = 0
for i in reversed(range(H)):
    cur = 0
    for j in reversed(range(W)):
        if a[i][j] == "#":
            cur = 0
            D[i][j] = 0
        else:
            cur += 1
            if i == (H-1):
                D[i][j] = 1
            else:
                D[i][j] += D[i+1][j] + 1
        R[i][j] = cur
        if L[i][j] + R[i][j] + D[i][j] + U[i][j] -3 > ans:
            ans = L[i][j] + R[i][j] + D[i][j] + U[i][j] -3

print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
H, W = map(int, input().split())

a = []
for i in range(H):
    a.append(str(input()))

R = [[0] * W for i in range(H)]
L = [[0] * W for i in range(H)]
D = [[0] * W for i in range(H)]
U = [[0] * W for i in range(H)]

for i in range(H):
    cur = 0
    for j in range(W):
        if a[i][j] == "#":
            cur = 0
            U[i][j] = 0
        else:
            cur += 1
            if i == 0:
                U[i][j] = 1
            else:
                U[i][j] += U[i-1][j] + 1
        L[i][j] = cur

ans = 0
for i in reversed(range(H)):
    cur = 0
    for j in reversed(range(W)):
        if a[i][j] == "#":
            cur = 0
            D[i][j] = 0
        else:
            cur += 1
            if i == (H-1):
                D[i][j] = 1
            else:
                D[i][j] += D[i+1][j] + 1
        R[i][j] = cur
        if L[i][j] + R[i][j] + D[i][j] + U[i][j] -3 > ans:
            ans = L[i][j] + R[i][j] + D[i][j] + U[i][j] -3

print(ans)

Fixed submission:
import sys
input=sys.stdin.readline

H, W = map(int, input().split())

a = []
for i in range(H):
    a.append(str(input()))

R = [[0] * W for i in range(H)]
L = [[0] * W for i in range(H)]
D = [[0] * W for i in range(H)]
U = [[0] * W for i in range(H)]

for i in range(H):
    cur = 0
    for j in range(W):
        if a[i][j] == "#":
            cur = 0
            U[i][j] = 0
        else:
            cur += 1
            if i == 0:
                U[i][j] = 1
            else:
                U[i][j] += U[i-1][j] + 1
        L[i][j] = cur

ans = 0
for i in reversed(range(H)):
    cur = 0
    for j in reversed(range(W)):
        if a[i][j] == "#":
            cur = 0
            D[i][j] = 0
        else:
            cur += 1
            if i == (H-1):
                D[i][j] = 1
            else:
                D[i][j] += D[i+1][j] + 1
        R[i][j] = cur
        if L[i][j] + R[i][j] + D[i][j] + U[i][j] -3 > ans:
            ans = L[i][j] + R[i][j] + D[i][j] + U[i][j] -3

print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
H, W = map(int, input().split())

a = []
for i in range(H):
    a.append(str(input()))

R = [[0] * W for i in range(H)]
L = [[0] * W for i in range(H)]
D = [[0] * W for i in range(H)]
U = [[0] * W for i in range(H)]

for i in range(H):
    cur = 0
    for j in range(W):
        if a[i][j] == "#":
            cur = 0
            U[i][j] = 0
        else:
            cur += 1
            if i == 0:
                U[i][j] = 1
            else:
                U[i][j] += U[i-1][j] + 1
        L[i][j] = cur

for i in reversed(range(H)):
    cur = 0
    for j in reversed(range(W)):
        if a[i][j] == "#":
            cur = 0
            D[i][j] = 0
        else:
            cur += 1
            if i == (H-1):
                D[i][j] = 1
            else:
                D[i][j] += D[i+1][j] + 1
        R[i][j] = cur

ans = 0
for i in range(H):
    for j in range(W):
        if L[i][j] + R[i][j] + D[i][j] + U[i][j] -3 > ans:
            ans = L[i][j] + R[i][j] + D[i][j] + U[i][j] -3

print(ans)

Fixed submission:
import sys
input=sys.stdin.readline

H, W = map(int, input().split())

a = []
for i in range(H):
    a.append(str(input()))

R = [[0] * W for i in range(H)]
L = [[0] * W for i in range(H)]
D = [[0] * W for i in range(H)]
U = [[0] * W for i in range(H)]

for i in range(H):
    cur = 0
    for j in range(W):
        if a[i][j] == "#":
            cur = 0
            U[i][j] = 0
        else:
            cur += 1
            if i == 0:
                U[i][j] = 1
            else:
                U[i][j] += U[i-1][j] + 1
        L[i][j] = cur

ans = 0
for i in reversed(range(H)):
    cur = 0
    for j in reversed(range(W)):
        if a[i][j] == "#":
            cur = 0
            D[i][j] = 0
        else:
            cur += 1
            if i == (H-1):
                D[i][j] = 1
            else:
                D[i][j] += D[i+1][j] + 1
        R[i][j] = cur
        if L[i][j] + R[i][j] + D[i][j] + U[i][j] -3 > ans:
            ans = L[i][j] + R[i][j] + D[i][j] + U[i][j] -3

print(ans)