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

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

    cnt = [0]*2
    for i in range(h):
        for j, a in enumerate(aa[i]):
            if a: continue
            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

    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
            if c0 < 2:
                return False
    return True

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