import sys
from collections import deque

def main():
    N, M = map(int, sys.stdin.readline().split())
    grid = [sys.stdin.readline().strip() for _ in range(N)]
    points = []
    for i in range(N):
        for j in range(M):
            if grid[i][j] == '.':
                points.append((i, j))
    K = len(points)
    if K % 2 != 0:
        print("NO")
        return
    if K == 0:
        print("NO")
        return
    # Check connectivity using BFS
    visited = set()
    q = deque()
    start = points[0]
    q.append(start)
    visited.add(start)
    dirs = [(-1, 0), (1, 0), (0, -1), (0, 1)]
    while q:
        i, j = q.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 (ni, nj) not in visited:
                    visited.add((ni, nj))
                    q.append((ni, nj))
    if len(visited) == K:
        print("YES")
    else:
        print("NO")

if __name__ == "__main__":
    main()