import sys
from collections import deque

def main():
    input = sys.stdin.read().split()
    n = int(input[0])
    m = int(input[1])
    grid = input[2:]
    
    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:
        print("NO")
        return
    
    if start is None:
        print("NO")
        return
    
    visited = [[False for _ in range(m)] for __ in range(n)]
    q = deque()
    q.append(start)
    visited[start[0]][start[1]] = True
    found = 1
    
    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 not visited[ni][nj]:
                    visited[ni][nj] = True
                    found += 1
                    q.append((ni, nj))
    
    if found == count:
        print("YES")
    else:
        print("NO")

if __name__ == "__main__":
    main()