Buggy python submission (verdict: Time Limit Exceeded):
# -*- coding: utf-8 -*-
"""
D - Lamp
https://atcoder.jp/contests/abc129/tasks/abc129_d

"""
import sys


def solve(H, W, grid):
    res_x = [[0]*W for _ in range(H)]
    x, y = 0, 0
    while y < H:
        while x < W:
            if grid[y][x] == '#':
                x += 1
                continue
            rx = x
            while rx < W and grid[y][rx] != '#':
                rx += 1
            for xx in range(x, rx):
                res_x[y][xx] = rx-x
            x = rx
        x = 0
        y += 1

    res_y = [[0]*W for _ in range(H)]
    x, y = 0, 0
    while x < W:
        while y < H:
            if grid[y][x] == '#':
                y += 1
                continue
            ry = y
            while ry < H and grid[ry][x] != '#':
                ry += 1
            for yy in range(y, ry):

                res_y[yy][x] = ry-y
            y = ry
        y = 0
        x += 1

    ans = 0
    for y in range(H):
        for x in range(W):
            t = res_x[y][x] + res_y[y][x] - 1
            if t > ans:
                ans = t
    return ans


def main(args):
    H, W = map(int, input().split())
    grid = [input() for _ in range(H)]
    ans = solve(H, W, grid)
    print(ans)


if __name__ == '__main__':
    main(sys.argv[1:])


Fixed submission:
# -*- coding: utf-8 -*-
"""



"""
import sys


def solve(H, W, grid):
    res_x = [[0]*W for _ in range(H)]
    x, y = 0, 0
    while y < H:
        while x < W:
            if grid[y][x] == '#':
                x += 1
                continue
            rx = x
            while rx < W and grid[y][rx] != '#':
                rx += 1
            for xx in range(x, rx):
                res_x[y][xx] = rx-x
            x = rx
        x = 0
        y += 1

    res_y = [[0]*W for _ in range(H)]
    x, y = 0, 0
    while y < H:
        while x < W:
            if grid[y][x] == '#' or res_y[y][x] != 0:
                x += 1
                continue
            dy = y
            while dy < H and grid[dy][x] != '#':
                dy += 1
            for yy in range(y, dy):
                if res_y[yy][x] == 0:
                    res_y[yy][x] = dy-y
            x += 1
        x = 0
        y += 1

    ans = 0
    for y in range(H):
        for x in range(W):
            t = res_x[y][x] + res_y[y][x] - 1
            if t > ans:
                ans = t
    return ans


def main(args):
    H, W = map(int, input().split())
    grid = [input() for _ in range(H)]
    ans = solve(H, W, grid)
    print(ans)


if __name__ == '__main__':
    main(sys.argv[1:])

Buggy python submission (verdict: Time Limit Exceeded):
# -*- coding: utf-8 -*-
"""
D - Lamp
https://atcoder.jp/contests/abc129/tasks/abc129_d

"""
import sys


def solve(H, W, grid):
    res_x = [[0]*W for _ in range(H)]
    x, y = 0, 0
    while y < H:
        while x < W:
            if grid[y][x] == '#':
                x += 1
                continue
            rx = x
            while rx < W and grid[y][rx] != '#':
                rx += 1
            for xx in range(x, rx):
                res_x[y][xx] = rx-x
            x = rx
        x = 0
        y += 1

    res_y = [[0]*W for _ in range(H)]
    x, y = 0, 0
    while y < H:
        while x < W:
            if grid[y][x] == '#' or res_y[y][x] != 0:
                x += 1
                continue
            dy = y
            while dy < H and grid[dy][x] != '#':
                dy += 1
            for yy in range(y, dy):
                if res_y[yy][x] == 0:
                    res_y[yy][x] = dy-y
            x += 1
        x = 0
        y += 1

    ans = 0
    for y in range(H):
        for x in range(W):
            t = res_x[y][x] + res_y[y][x] - 1
            if t > ans:
                ans = t
    return ans


def main(args):
    H, W = map(int, input().split())
    grid = [input() for _ in range(H)]
    ans = solve(H, W, grid)
    print(ans)


if __name__ == '__main__':
    main(sys.argv[1:])


Fixed submission:
# -*- coding: utf-8 -*-
"""



"""
import sys


def solve(H, W, grid):
    res_x = [[0]*W for _ in range(H)]
    x, y = 0, 0
    while y < H:
        while x < W:
            if grid[y][x] == '#':
                x += 1
                continue
            rx = x
            while rx < W and grid[y][rx] != '#':
                rx += 1
            for xx in range(x, rx):
                res_x[y][xx] = rx-x
            x = rx
        x = 0
        y += 1

    res_y = [[0]*W for _ in range(H)]
    x, y = 0, 0
    while y < H:
        while x < W:
            if grid[y][x] == '#' or res_y[y][x] != 0:
                x += 1
                continue
            dy = y
            while dy < H and grid[dy][x] != '#':
                dy += 1
            for yy in range(y, dy):
                if res_y[yy][x] == 0:
                    res_y[yy][x] = dy-y
            x += 1
        x = 0
        y += 1

    ans = 0
    for y in range(H):
        for x in range(W):
            t = res_x[y][x] + res_y[y][x] - 1
            if t > ans:
                ans = t
    return ans


def main(args):
    H, W = map(int, input().split())
    grid = [input() for _ in range(H)]
    ans = solve(H, W, grid)
    print(ans)


if __name__ == '__main__':
    main(sys.argv[1:])

Buggy python submission (verdict: Time Limit Exceeded):
# -*- coding: utf-8 -*-
"""



"""
import sys


def solve(H, W, grid):
    res_x = [[0]*W for _ in range(H)]
    x, y = 0, 0
    while y < H:
        while x < W:
            if grid[y][x] == '#':
                x += 1
                continue
            rx = x
            while rx < W and grid[y][rx] != '#':
                rx += 1
            for xx in range(x, rx):
                res_x[y][xx] = rx-x
            x = rx
        x = 0
        y += 1

    res_y = [[0]*W for _ in range(H)]
    x, y = 0, 0
    while y < H:
        while x < W:
            if grid[y][x] == '#':
                x += 1
                continue
            dy = y
            while dy < H and grid[dy][x] != '#':
                dy += 1
            for yy in range(y, dy):
                if res_y[yy][x] == 0:
                    res_y[yy][x] = dy-y
            x += 1
        x = 0
        y += 1

    ans = 0
    for y in range(H):
        for x in range(W):
            t = res_x[y][x] + res_y[y][x] - 1
            if t > ans:
                ans = t
    return ans


def main(args):
    H, W = map(int, input().split())
    grid = [input() for _ in range(H)]
    ans = solve(H, W, grid)
    print(ans)


if __name__ == '__main__':
    main(sys.argv[1:])


Fixed submission:
# -*- coding: utf-8 -*-
"""



"""
import sys


def solve(H, W, grid):
    res_x = [[0]*W for _ in range(H)]
    x, y = 0, 0
    while y < H:
        while x < W:
            if grid[y][x] == '#':
                x += 1
                continue
            rx = x
            while rx < W and grid[y][rx] != '#':
                rx += 1
            for xx in range(x, rx):
                res_x[y][xx] = rx-x
            x = rx
        x = 0
        y += 1

    res_y = [[0]*W for _ in range(H)]
    x, y = 0, 0
    while y < H:
        while x < W:
            if grid[y][x] == '#' or res_y[y][x] != 0:
                x += 1
                continue
            dy = y
            while dy < H and grid[dy][x] != '#':
                dy += 1
            for yy in range(y, dy):
                if res_y[yy][x] == 0:
                    res_y[yy][x] = dy-y
            x += 1
        x = 0
        y += 1

    ans = 0
    for y in range(H):
        for x in range(W):
            t = res_x[y][x] + res_y[y][x] - 1
            if t > ans:
                ans = t
    return ans


def main(args):
    H, W = map(int, input().split())
    grid = [input() for _ in range(H)]
    ans = solve(H, W, grid)
    print(ans)


if __name__ == '__main__':
    main(sys.argv[1:])

Buggy python submission (verdict: Time Limit Exceeded):
# -*- coding: utf-8 -*-
"""



"""
import sys


def solve(H, W, grid):
    res_x = [[0]*W for _ in range(H)]
    x, y = 0, 0
    while y < H:
        while x < W:
            if grid[y][x] == '#':
                x += 1
                continue
            rx = x
            while rx < W and grid[y][rx] != '#':
                rx += 1
            for xx in range(x, rx):
                res_x[y][xx] = rx-x
            x = rx
        x = 0
        y += 1

    res_y = [[0]*W for _ in range(H)]
    x, y = 0, 0
    while y < H:
        while x < W:
            if grid[y][x] == '#':
                x += 1
                continue
            dy = y
            while dy < H and grid[dy][x] != '#':
                dy += 1
            for yy in range(y, dy):
                if res_y[yy][x] == 0:
                    res_y[yy][x] = dy-y
            x += 1
        x = 0
        y += 1

    ans = 0
    for y in range(H):
        for x in range(W):
            t = res_x[y][x] + res_y[y][x] - 1
            if t > ans:
                ans = t
    return ans


def main(args):
    H, W = map(int, input().split())
    grid = [input() for _ in range(H)]
    ans = solve(H, W, grid)
    print(ans)


if __name__ == '__main__':
    main(sys.argv[1:])


Fixed submission:
# -*- coding: utf-8 -*-
"""



"""
import sys


def solve(H, W, grid):
    res_x = [[0]*W for _ in range(H)]
    x, y = 0, 0
    while y < H:
        while x < W:
            if grid[y][x] == '#':
                x += 1
                continue
            rx = x
            while rx < W and grid[y][rx] != '#':
                rx += 1
            for xx in range(x, rx):
                res_x[y][xx] = rx-x
            x = rx
        x = 0
        y += 1

    res_y = [[0]*W for _ in range(H)]
    x, y = 0, 0
    while y < H:
        while x < W:
            if grid[y][x] == '#' or res_y[y][x] != 0:
                x += 1
                continue
            dy = y
            while dy < H and grid[dy][x] != '#':
                dy += 1
            for yy in range(y, dy):
                if res_y[yy][x] == 0:
                    res_y[yy][x] = dy-y
            x += 1
        x = 0
        y += 1

    ans = 0
    for y in range(H):
        for x in range(W):
            t = res_x[y][x] + res_y[y][x] - 1
            if t > ans:
                ans = t
    return ans


def main(args):
    H, W = map(int, input().split())
    grid = [input() for _ in range(H)]
    ans = solve(H, W, grid)
    print(ans)


if __name__ == '__main__':
    main(sys.argv[1:])