#include <bits/stdc++.h>

using namespace std;

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()

template<typename A, typename B> inline bool chmax(A &a, B b) { if (a<b) { a=b; return 1; } return 0; }
template<typename A, typename B> inline bool chmin(A &a, B b) { if (a>b) { a=b; return 1; } return 0; }

typedef unsigned long long ull;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<int, pii> P;

const ll INF = 1ll<<29;
const ll MOD = 1000000007;
const double EPS  = 1e-10;

int h, w;
string maps[50];
bool done[50][50];

int main() {
	cin >> h >> w;
	REP(i, h) cin >> maps[i];
	
	bool ans = false;
	
	REP(dy, h) REP(dx, w) {
		if (dx == 0 && dy == 0) continue;
		
		REP(i, h) REP(j, w) done[i][j] = maps[i][j] == '.';
		
		bool ok = true;
		
		REP(i, h) REP(j, w) {
			if (done[i][j]) continue;
			
			int ny = i + dy, nx = j + dx;
			
			bool ng = false;
			
			if (!(nx >= 0 && nx < w && ny >= 0 && ny < h)) ng = true;
			if (!ng && done[ny][nx]) ng = true;
			
			if (!ng) done[ny][nx] = true;
			
			if (ng) ok = false;
		}
		
		if (ok) ans = true;
	}
	
	puts(ans ? "YES" : "NO");
	
	return 0;
}