import java.util.Scanner;

public class Yukicoder85 {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt(), m = sc.nextInt();
		String[] a = new String[n];
		for (int i = 0; i < n; i++) a[i] = sc.next();

		int oddCount = 0, buf;
		for (int i = 0; i < n; i++) {
			for (int j = 0; j < m; j++) {
				if (a[i].charAt(j) == '#') continue;
				buf = 0;
				if (i - 1 >= 0) buf += a[i - 1].charAt(j) == '.' ? 1 : 0;
				if (i + 1 < n) buf += a[i + 1].charAt(j) == '.' ? 1 : 0;
				if (j - 1 >= 0) buf += a[i].charAt(j - 1) == '.' ? 1 : 0;
				if (j + 1 < m) buf += a[i].charAt(j + 1) == '.' ? 1 : 0;
				if (buf % 2 == 0) oddCount++;
			}
		}
		if (oddCount % 2 == 0)
			System.out.println("YES");
		else 
			System.out.println("NO");
	}
}