import sys

# sys.setrecursionlimit(200005)
int1 = lambda x: int(x)-1
pDB = lambda *x: print(*x, end="\n", file=sys.stderr)
p2D = lambda x: print(*x, sep="\n", end="\n\n", file=sys.stderr)
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()

dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
inf = (1 << 63)-1
# inf = (1 << 31)-1
md = 10**9+7
# md = 998244353

class UnionFind:
    def __init__(self, n):
        self.state = [-1]*n
        self.size_table = [1]*n
        self.cnt = n

    def root(self, u):
        stack = []
        while self.state[u] >= 0:
            stack.append(u)
            u = self.state[u]
        for v in stack: self.state[v] = u
        return u

    def same(self, u, v):
        return self.root(u) == self.root(v)

    def merge(self, u, v):
        u = self.root(u)
        v = self.root(v)
        if u == v: return False
        du = -self.state[u]
        dv = -self.state[v]
        if du < dv: u, v = v, u
        if du == dv: self.state[u] -= 1
        self.state[v] = u
        self.cnt -= 1
        self.size_table[u] += self.size_table[v]
        return True

    def size(self, u):
        return self.size_table[self.root(u)]

def ok():
    h, w = LI()
    aa = [[c == "#" for c in SI()] for _ in range(h)]

    cnt = [0]*2
    gi = gj = -1
    for i in range(h):
        for j, a in enumerate(aa[i]):
            if a: continue
            gi, gj = i, j
            cnt[(i+j) & 1] += 1
    if cnt[0] != cnt[1]:
        return False

    if cnt[0] == 1:
        for i in range(h):
            for j, a in enumerate(aa[i]):
                if a: continue
                for di, dj in dij:
                    ni, nj = i+di, j+dj
                    if ni < 0 or nj < 0 or ni >= h or nj >= w: continue
                    if aa[ni][nj] == 0: return True
                return False

    uf = UnionFind(h*w)
    for i in range(h):
        for j, a in enumerate(aa[i]):
            if a: continue
            c0 = 0
            for di, dj in dij:
                ni, nj = i+di, j+dj
                if ni < 0 or nj < 0 or ni >= h or nj >= w: continue
                if aa[ni][nj]: continue
                c0 += 1
                uf.merge(i*w+j, ni*w+nj)
            if c0 < 2:
                return False

    return uf.size(gi*w+gj) == sum(cnt)

print("YES" if ok() else "NO")