#include <bits/stdc++.h>
using namespace std;
using LL = long long int;
#define incID(i, l, r) for(int i = (l)    ; i <  (r); ++i)
#define decID(i, l, r) for(int i = (r) - 1; i >= (l); --i)
#define incII(i, l, r) for(int i = (l)    ; i <= (r); ++i)
#define decII(i, l, r) for(int i = (r)    ; i >= (l); --i)
#define inc(i, n)  incID(i, 0, n)
#define dec(i, n)  decID(i, 0, n)
#define inc1(i, n) incII(i, 1, n)
#define dec1(i, n) decII(i, 1, n)
#define inID(v, l, r) ((l) <= (v) && (v) <  (r))
#define inII(v, l, r) ((l) <= (v) && (v) <= (r))
#define PB push_back
#define EB emplace_back
#define MP make_pair
#define FI first
#define SE second
#define FR front()
#define BA back()
#define ALL(v) v.begin(), v.end()
#define RALL(v) v.rbegin(), v.rend()
auto setmin   = [](auto & a, auto b) { return (b <  a ? a = b, true : false); };
auto setmax   = [](auto & a, auto b) { return (b >  a ? a = b, true : false); };
auto setmineq = [](auto & a, auto b) { return (b <= a ? a = b, true : false); };
auto setmaxeq = [](auto & a, auto b) { return (b >= a ? a = b, true : false); };
#define SI(v) static_cast<int>(v.size())
#define RF(e, v) for(auto & e: v)
#define until(e) while(! (e))
#define if_not(e) if(! (e))
#define ef else if
#define UR assert(false)
#define IN(T, ...) T __VA_ARGS__; IN_(__VA_ARGS__);
void IN_() { };
template<typename T, typename ... U> void IN_(T & a, U & ... b) { cin >> a; IN_(b ...); };
template<typename T> void OUT(T && a) { cout << a << endl; }
template<typename T, typename ... U> void OUT(T && a, U && ... b) { cout << a << " "; OUT(b ...); }

// ---- ----

template<typename T> istream & operator>>(istream & s, vector<T> & v) { RF(e, v) { s >> e; } return s; }
template<typename T> ostream & operator<<(ostream & s, vector<T> const & v) {
	inc(i, SI(v)) { s << (i == 0 ? "" : " ") << v[i]; }
	return s;
}

int main() {
	IN(int, h, w);
	vector<string> s(h);
	cin >> s;
	
	auto no = [&]() { OUT("NO"); exit(0); };
	
	int imi = h, ima = -1, jmi = w, jma = -1;
	inc(i, h) {
	inc(j, w) {
		if_not(s[i][j] == '.') { continue; }
		setmin(imi, i);
		setmax(ima, i);
		setmin(jmi, j);
		setmax(jma, j);
	}
	}
	if(imi == ima || jmi == jma) { no(); }
	
	bool A = (s[imi][jmi] == '.');
	bool B = (s[ima][jmi] == '.');
	bool C = (s[ima][jma] == '.');
	bool D = (s[imi][jma] == '.');
	int c = 0;
	if(! A) { c++; }
	if(! B) { c++; }
	if(! C) { c++; }
	if(! D) { c++; }
	if(c > 1) { no(); }
	
	auto rot = [&]() {
		vector<string> t(w, string(h, '-'));
		inc(i, h) {
		inc(j, w) {
			t[j][h - 1 - i] = s[i][j];
		}
		}
		
		swap(imi, jmi);
		swap(ima, jma);
		jmi = h - 1 - jmi;
		jma = h - 1 - jma;
		swap(jmi, jma);
		swap(h, w);
		s = t;
	};
	
	if(! A) { }
	if(! B) { rot(); }
	if(! C) { rot(); rot(); }
	if(! D) { rot(); rot(); rot(); }
	
	vector<string> t(h, string(w, '#'));
	inc(i, h) {
	inc(j, w) {
		if(
			((i == imi || i == ima) && inII(j, jmi, jma)) ||
			((j == jmi || j == jma) && inII(i, imi, ima))
		) { t[i][j] = '.'; }
	}
	}
	if(c == 1) {
		int ii = imi, jj = jmi;
		until(s[ii][jmi] == '.') { ii++; }
		until(s[imi][jj] == '.') { jj++; }
		if(ii == ima || jj == jma) { no(); }
		inc(i, ii) {
		inc(j, jj) {
			t[i][j] = '#';
		}
		}
		incII(i, imi, ii) { t[i][jj] = '.'; }
		incII(j, jmi, jj) { t[ii][j] = '.'; }
	}
	if(s == t) { OUT("YES"); } else { no(); }
}