import sys
import math


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


def main():
    N, M = map(int, input().split())
    A = [input() for i in range(N)]

    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 cnt != 2*(maxi-mini) + 2*(maxj-minj):
        print('NO')
        return

    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():
        print('YES')
        return

    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:
            redi = i
            if redi is not None:
                print('NO')
                return
        if cnt < 2:
            print('NO')
            return

    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:
                print('NO')
                return
            redj = j
        if cnt < 2:
            print('NO')
            return

    if redi is None or redj is None:
        print('NO')
        return

    def checku():
        for i in range(mini, redi+1):
            if A[i][redj] == '#':
                return False
        return True

    def checkd():
        for i in range(redi, maxi+1):
            if A[i][redj] == '#':
                return False
        return True

    def checkl():
        for j in range(minj, redj+1):
            if A[redi][j] == '#':
                return False
        return True

    def checkr():
        for j in range(redj, maxj+1):
            if A[redi][j] == '#':
                return False
            return True

    if (checku() or checkd()) and (checkl() or checkr()):
        print('YES')
    else:
        print('NO')


if __name__ == '__main__':
    main()