#define _USE_MATH_DEFINES
#include <algorithm>
#include <cstdio>
#include <functional>
#include <iostream>
#include <cfloat>
#include <climits>
#include <cstring>
#include <cmath>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <time.h>
#include <vector>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> i_i;
typedef pair<ll, int> ll_i;
typedef pair<double, int> d_i;
typedef pair<ll, ll> ll_ll;
typedef pair<double, double> d_d;
struct edge { int u, v; ll w; };

ll MOD = 1000000007;
ll _MOD = 1000000009;
double EPS = 1e-10;

int main() {
	int N, M; cin >> N >> M;
	vector<string> A(N);
	for (int i = 0; i < N; i++) cin >> A[i];
	int cnt = 0, l = M, r = 0, u = N, d = 0;
	for (int i = 0; i < N; i++)
		for (int j = 0; j < M; j++)
			if (A[i][j] == '.') {
				cnt++;
				l = min(l, j);
				r = max(r, j + 1);
				u = min(u, i);
				d = max(d, i + 1);
			}
	if (cnt == (r - l + d - u) * 2 - 4)
		cout << "YES" << endl;
	else
		cout << "NO" << endl;
}