def read_data():
    H, W = map(int, input().split())
    S = [input() for i in range(H)]
    return H, W, S

def solve(H, W, S):
    dist = [[-1] * W for i in range(H)]
    for h in range(H):
        d = 0
        Sh = S[h]
        disth = dist[h]
        for w, c in enumerate(Sh):
            if c == '#':
                d += 1
                if disth[w] == -1 or disth[w] > d:
                    disth[w] = d
            else:
                d = 0
    for h in range(H):
        d = 0
        Sh = S[h]
        disth = dist[h]
        for w in range(W-1, -1, -1):
            c = Sh[w]
            if c == '#':
                d += 1
                if disth[w] == -1 or disth[w] > d:
                    disth[w] = d
            else:
                d = 0
    for w in range(W):
        d = 0
        Sw = S[w]
        distw = dist[w]
        for h, c in enumerate(Sw):
            if c == '#':
                d += 1
                if distw[h] == -1 or distw[h] > d:
                    distw[h] = d
            else:
                d = 0
    for w in range(W):
        d = 0
        Sw = S[w]
        distw = dist[w]
        for h in range(H-1, -1, -1):
            if c == '#':
                d += 1
                if distw[h] == -1 or distw[h] > d:
                    distw[h] = d
            else:
                d = 0
    maxd = 0
    for row in dist:
        maxd = max(maxd, max(row))
    return maxd

H, W, S = read_data()
print(solve(H, W, S))