H,W = (int(i) for i in input().split())
s = [[-1] * (W + 2) for i in range(H+2)]
t = [[-1] * (W + 2) for i in range(H+2)]
 
for i in range(1, H+1):
    SS = input()
    for j in range(W):
        if SS[j] == "#":
            s[i][j+1] = -1
            t[i][j+1] = -1
        else:
            s[i][j+1] = 0
            t[i][j+1] = 0
 
tmp = []
num = 0
for i in range(1, H+1):
    for j in range(1, W+2):
        if s[i][j] == -1 :
            if num != 0:
                for tp in tmp:
                    s[i][tp] = num
                tmp = []
                num =0
        else:
            tmp.append(j)
            num += 1
 
tmp = []
num = 0
for j in range(1, W+1):
    for i in range(1, H+2):
        if t[i][j] == -1 :
            if num != 0:
                for tp in tmp:
                    t[tp][j] = num
                tmp = []
                num =0
        else:
            tmp.append(i)
            num += 1
 
ref = 0
for i in range(H+2):
    for j in range(W+2):
        ref = max(s[i][j] + t[i][j], ref)
 
print(ref-1)