import sys
import math


def input(): return sys.stdin.readline().rstrip()


def check(A):
    N = len(A)
    M = len(A[0])

    mini = minj = math.inf
    maxi = maxj = -math.inf
    cnt = 0
    for i in range(N):
        for j in range(M):
            if A[i][j] == '.':
                cnt += 1
                mini, minj, maxi, maxj = \
                    min(mini, i), min(minj, j), max(maxi, i), max(maxj, j)

    if maxi == mini or maxj == minj:
        return False

    if cnt != 2*(maxi-mini) + 2*(maxj-minj):
        return False

    def checkrect():
        for i in range(mini, maxi+1):
            if A[i][minj] == '#' or A[i][maxj] == '#':
                return False
        for j in range(minj, maxj+1):
            if A[mini][j] == '#' or A[maxi][j] == '#':
                return False
        return True

    if checkrect():
        return False

    redi = redj = None
    for i in range(mini+1, maxi):
        cnt = 0
        for j in range(minj, maxj+1):
            if A[i][j] == '.':
                cnt += 1
        if cnt > 2:
            if redi is not None:
                return False
            redi = i
        if cnt < 2:
            return False

    for j in range(minj+1, maxj):
        cnt = 0
        for i in range(mini, maxi+1):
            if A[i][j] == '.':
                cnt += 1
        if cnt > 2:
            if redj is not None:
                return False
            redj = j
        if cnt < 2:
            return False

    if redi is None or redj is None:
        return False

    for i in range(N):
        for j in range(M):
            if A[i][j] == '.':
                if i == maxi:
                    continue
                if j == mini:
                    continue
                if i == mini and minj <= j <= redj:
                    continue
                if i == redi and redj <= j <= maxj:
                    continue
                if j == redj and mini <= i <= redi:
                    continue
                if j == maxj and redi <= i <= maxi:
                    continue
                return False
    return True


def main():
    N, M = map(int, input().split())
    A = [input() for i in range(N)]
    for i in range(4):
        if check(A):
            print('YES')
            return
        *A, = zip(*A[::-1])

    print('NO')


if __name__ == '__main__':
    main()