def main():
    import sys
    from collections import deque

    N, M = map(int, sys.stdin.readline().split())
    grid = [sys.stdin.readline().strip() for _ in range(N)]

    # Count the number of viewable cells
    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 == 0:
        print("NO")
        return

    if count % 2 != 0:
        print("NO")
        return

    # Check if all '.' are connected
    visited = [[False for _ in range(M)] for _ in range(N)]
    queue = deque()
    queue.append(start)
    visited[start[0]][start[1]] = True

    dirs = [(0, 1), (1, 0), (0, -1), (-1, 0)]  # right, down, left, up

    while queue:
        i, j = queue.popleft()
        for di, dj in dirs:
            ni, nj = i + di, j + dj
            if 0 <= ni < N and 0 <= nj < M:
                if grid[ni][nj] == '.' and not visited[ni][nj]:
                    visited[ni][nj] = True
                    queue.append((ni, nj))

    # Verify all '.' are visited
    for i in range(N):
        for j in range(M):
            if grid[i][j] == '.' and not visited[i][j]:
                print("NO")
                return

    # Check grid dimensions
    if N >= 2 and M >= 2:
        print("YES")
    else:
        print("NO")

if __name__ == "__main__":
    main()