#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <stack>
#include <queue>
#include <list>
#include <set>
#include <map>
#include <numeric>
#include <regex>
#include <tuple>
#include<iomanip>
using namespace std;

typedef long long ll;
typedef pair<int, int> P;
#define MOD 1000000007 // 10^9 + 7
#define INF 1000000000 // 10^9
#define LLINF 1LL<<60

bool white[59][59];

int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);

	int H, W; cin >> H >> W;
	P start; start.first = -1; start.second = -1;

	for (int i = 1; i <= H; i++) {
		for (int j = 1; j <= W; j++) {
			char c; cin >> c;
			if (c == '.') white[i][j] = true;
			if (start.first == -1) {
				start.first = i;
				start.second = j;
			}
		}
	}

	for (int dx = 0; dx <= H - start.first; dx++) {
		for (int dy = -start.second+1; dy <= W - start.second; dy++) {
			if (!(dx == 0 && dy == 0)&& !white[start.first + dx][start.second + dy]) {

				bool field[59][59];
				for (int i = 1; i <= H; i++) {
					for (int j = 1; j <= W; j++) field[i][j] = white[i][j];
				}
				bool flag = true;

				for (int i = 1; i <= H && flag; i++) {
					for (int j = 1; j <= W && flag; j++) {
						if (!field[i][j]) { // 元が黒で
							if (i + dx > H || j + dy > W || j + dy < 1) flag = false;
							else {
								if (field[i + dx][j + dy]) {// 平行移動先が白
									flag = false;
								}
								else { // 平行移動先も黒
									field[i][j] = true;
									field[i + dx][j + dy] = true;
								}
							}
						}
					}
				}

				if (flag) {
					cout << "YES" << endl;
					return 0;
				}

			}
		}
	}
	cout << "NO" << endl;

	return 0;
}