// includes
#include <bits/stdc++.h>

// macros
#define ll long long int
#define pb emplace_back
#define mk make_pair
#define pq priority_queue
#define FOR(i, a, b) for(int i=(a);i<(b);++i)
#define rep(i, n) FOR(i, 0, n)
#define rrep(i, n) for(int i=((int)(n)-1);i>=0;i--)
#define all(x) (x).begin(),(x).end()
#define sz(x) ((int)(x).size())
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end())
#define FI first
#define SE second
using namespace std;

//  types
typedef pair<int, int> P;
typedef pair<ll, int> Pl;
typedef pair<ll, ll> Pll;
typedef pair<double, double> Pd;
 
// constants
const int inf = 1e9;
const ll linf = 1LL << 50;
const double EPS = 1e-10;
const int mod = 1e9 + 7;

// solve
template <class T>bool chmax(T &a, const T &b){if(a < b){a = b; return 1;} return 0;}
template <class T>bool chmin(T &a, const T &b){if(a > b){a = b; return 1;} return 0;}
template <typename T> istream &operator>>(istream &is, vector<T> &vec){for(auto &v: vec)is >> v; return is;}

string s[101];

int main(int argc, char const* argv[])
{
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  int n, m;
  cin >> n >> m;
  rep(i, n)cin >> s[i];
  int xmax = -1, xmin = n + 1, ymax = -1, ymin = m + 1;
  int all = 0;
  rep(i, n){
    rep(j, m){
      if(s[i][j] == '#')continue;
      xmax = max(xmax, i);
      xmin = min(xmin, i);
      ymax = max(ymax, j);
      ymin = min(ymin, j);
      all++;
    }
  }
  int tall = 0;
  bool b[4] = {true, true, true, true};
  for(int i = xmin; i <= xmax; i++){
    b[0] &= (s[i][ymin] == '.');
    b[2] &= (s[i][ymax] == '.');
    tall += 2;
  }
  for(int i = ymin; i <= ymax; i++){
    b[1] &= (s[xmin][i] == '.');
    b[3] &= (s[xmax][i] == '.');
    tall += 2;
  }
  if(xmax == xmin || ymax == ymin){
    cout << "NO" << endl;
    return 0;
  }
  tall -= 4;
  int cnt = 0;
  if(all != tall){
    cout << "NO" << endl;
    return 0;
  }
  rep(i, 4)if(b[i])cnt++;
  if(cnt == 4){
    cout << "YES" << endl;
    return 0;
  }else if(cnt < 2){
    cout << "NO" << endl;
    return 0;
  }
  bool res = true;
  if(s[xmin][ymin] != '.'){
    int i = xmin, j = ymin;
    while(s[i][ymin] == '#')i++;
    while(s[xmin][j] == '#')j++;
    if(i == n - 1 || j == m - 1)res = false;
    for(int k = i; k <= xmax; k++)res &= (s[k][ymin] == '.');
    for(int k = j; k <= ymax; k++)res &= (s[xmin][k] == '.');
    for(int k = ymin; k <= j; k++)res &= (s[i][k] == '.');
    for(int k = xmin; k <= i; k++)res &= (s[k][j] == '.');
  }else if(s[xmin][ymax] != '.'){
    int i = xmin, j = ymax;
    while(s[i][ymax] == '#')i++;
    while(s[xmin][j] == '#')j--;
    if(i == n - 1 || j == 0)res = false;
    for(int k = i; k <= xmax; k++)res &= (s[k][ymax] == '.');
    for(int k = j; k >= ymin; k--)res &= (s[xmin][k] == '.');
    for(int k = ymax; k >= j; k--)res &= (s[i][k] == '.');
    for(int k = xmin; k <= i; k++)res &= (s[k][j] == '.');
  }else if(s[xmax][ymin] != '.'){
    int i = xmax, j = ymin;
    while(s[i][ymin] == '#')i--;
    while(s[xmax][j] == '#')j++;
    if(i == 0 || j == m - 1)res = false;
    for(int k = i; k >= xmin; k--)res &= (s[k][ymin] == '.');
    for(int k = j; k <= ymax; k++)res &= (s[xmax][k] == '.');
    for(int k = ymin; k <= j; k++)res &= (s[i][k] == '.');
    for(int k = xmax; k >= i; k--)res &= (s[k][j] == '.');
  }else{
    int i = xmax, j = ymax;
    while(s[i][ymax] == '#')i--;
    while(s[xmax][j] == '#')j--;
    if(i == 0 || j == 0)res = false;
    for(int k = i; k >= xmin; k--)res &= (s[k][ymax] == '.');
    for(int k = j; k >= ymin; k--)res &= (s[xmax][k] == '.');
    for(int k = ymax; k >= j; k--)res &= (s[i][k] == '.');
    for(int k = xmax; k >= i; k--)res &= (s[k][j] == '.');
  }
  if(res)cout << "YES" << endl;
  else cout << "NO" << endl;
	return 0;
}