n, m = map(int, input().split())
grid = [input().strip() for _ in range(n)]

count = 0
start = None
for i in range(n):
    for j in range(m):
        if grid[i][j] == '.':
            count += 1
            if start is None:
                start = (i, j)

if count % 2 != 0 or count == 0:
    print("NO")
else:
    visited = [[False]*m for _ in range(n)]
    from collections import deque
    q = deque()
    if start:
        q.append(start)
        visited[start[0]][start[1]] = True
    found = 0
    dirs = [(-1,0), (1,0), (0,-1), (0,1)]
    while q:
        i, j = q.popleft()
        found += 1
        for di, dj in dirs:
            ni, nj = i + di, j + dj
            if 0 <= ni < n and 0 <= nj < m and not visited[ni][nj] and grid[ni][nj] == '.':
                visited[ni][nj] = True
                q.append((ni, nj))
    print("YES" if found == count else "NO")