import sys
from collections import deque

def main():
    input = sys.stdin.read().split()
    idx = 0
    N = int(input[idx])
    idx += 1
    M = int(input[idx])
    idx += 1
    grid = []
    viewable = []
    total = 0
    start = None
    for i in range(N):
        line = input[idx]
        idx += 1
        grid.append(line)
        for j in range(M):
            if line[j] == '.':
                total += 1
                if start is None:
                    start = (i, j)
    
    if total % 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
    count = 1
    
    dirs = [(-1, 0), (1, 0), (0, -1), (0, 1)]
    
    while q:
        i, j = q.popleft()
        for di, dj in dirs:
            ni = i + di
            nj = j + dj
            if 0 <= ni < N and 0 <= nj < M:
                if grid[ni][nj] == '.' and not visited[ni][nj]:
                    visited[ni][nj] = True
                    count += 1
                    q.append((ni, nj))
    
    if count == total:
        print("YES")
    else:
        print("NO")

if __name__ == "__main__":
    main()