import java.util.Scanner;

public class No179 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int h = Integer.parseInt(sc.next());
        int w = Integer.parseInt(sc.next());
        String s;
        int first = 0, trans = 0, diff = 0, count = 0, check = 0;
        boolean[] b = new boolean[h*w];
        for (int i = 0; i < h; i++) {
            s = sc.next();
            for (int j = 0; j < w; j++) {
                if(s.charAt(j) == '#'){
                    b[i*w+j] = true;
                    count++;
                }
            }
        }

        if(count % 2 == 1){
            System.out.println("NO");
            return;
        }
        count /= 2;

        for (int i = 0; i < h * w; i++) {
            if(b[i]){
                first = i;
                break;
            }
        }

        for (int i = first + 1; i < h * w; i++) {
            if(b[i]){
                trans = i;
                diff = trans - first;
                check = 0;
                for (int j = first + 1; j < h * w; j++) {
                    if(b[j] && j != trans){
                        if(j+diff >= h*w || !b[j+diff]){
                            break;
                        }
                        check++;
                    }
                    if(check == count / 2){
                        System.out.println("YES");
                        return;
                    }
                }
            }
        }
        System.out.println("NO");
        return;
    }
}