// includes
#include <bits/stdc++.h>
using namespace std;

// macros
#define pb emplace_back
#define mk make_pair
#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 irep(itr, st) for(auto itr = (st).begin(); itr != (st).end(); ++itr)
#define irrep(itr, st) for(auto itr = (st).rbegin(); itr != (st).rend(); ++itr)
#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 bit(n) (1LL<<(n))
// functions
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;}
template <typename T> ostream &operator<<(ostream &os, const vector<T>& vec){for(int i = 0; i < vec.size(); i++){ os << vec[i]; if(i + 1 != vec.size())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const set<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const unordered_set<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const multiset<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const unordered_multiset<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &p){os << p.first << " " << p.second; return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const map<T1, T2> &mp){for(auto itr = mp.begin(); itr != mp.end(); ++itr){ os << itr->first << ":" << itr->second; auto titr = itr; if(++titr != mp.end())os << " "; } return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const unordered_map<T1, T2> &mp){for(auto itr = mp.begin(); itr != mp.end(); ++itr){ os << itr->first << ":" << itr->second; auto titr = itr; if(++titr != mp.end())os << " "; } return os;}
//  types
using ll = long long int;
using P = pair<int, int>;
// constants
const int inf = 1e9;
const ll linf = 1LL << 50;
const double EPS = 1e-10;
const int mod = 1000000007;
const int dx[4] = {-1, 0, 1, 0};
const int dy[4] = {0, -1, 0, 1};
// io
struct fast_io{
  fast_io(){ios_base::sync_with_stdio(false); cin.tie(0); cout << fixed << setprecision(20);}
} fast_io_;

string s[101];
string t[101];

int h, w;

void rotate(){
  rep(i, w)t[i] = string(h, '#');
  rep(i, h)rep(j, w){
    t[w-j-1][i] = s[i][j];
  }
  swap(s, t);
  swap(h, w);
}

int main(int argc, char const* argv[])
{
  cin >> h >> w;
  rep(i, h)cin >> s[i];
  int xmax = -1, xmin = h + 1, ymax = -1, ymin = w + 1;
  int cnt = 0;
  rep(i, h)rep(j, w){
    if(s[i][j] == '.'){
      cnt++;
      xmax = max(xmax, i);
      xmin = min(xmin, i);
      ymax = max(ymax, j);
      ymin = min(ymin, j);
    }
  }
  if(xmin == xmax || ymin == ymax){
    cout << "NO" << endl;
    return 0;
  }
  int all = (xmax - xmin + 1) * 2 + (ymax - ymin + 1) * 2 - 4;
  bool ok = true;
  for(int i = xmin; i <= xmax; i++)if(s[i][ymin] == '#')ok = false;
  for(int i = xmin; i <= xmax; i++)if(s[i][ymax] == '#')ok = false;
  for(int i = ymin; i <= ymax; i++)if(s[xmax][i] == '#')ok = false;
  for(int i = ymin; i <= ymax; i++)if(s[xmin][i] == '#')ok = false;
  if(ok && all == cnt){
    cout << "YES" << endl;
    return 0;
  }
  rep(i_, 4){
    bool ok = true;
    for(int i = xmin; i <= xmax; i++)if(s[i][ymin] == '#')ok = false;
    for(int j = ymin; j <= ymax; j++)if(s[xmax][j] == '#')ok = false;
    int i = xmax;
    while(i > xmin){
      if(s[i][ymax] == '#'){
        i++;
        break;
      }
      i--;
    }
    if(i == xmin)i++;
    int j = ymax;
    while(j > ymin){
      if(s[i][j] == '#'){
        j++;
        break;
      }
      j--;
    }
    if(j == ymin)j++;
    for(int k = i; k >= xmin; k--)if(s[k][j] == '#')ok = false;
    for(int k = j; k >= ymin; k--)if(s[xmin][k] == '#')ok = false;
    int al = (xmax - xmin + 1) + (ymax - ymin) + xmax - i + ymax - j + i - xmin + j - ymin - 1;
    if(ok && al == cnt){
      cout << "YES" << endl;
      return 0;
    }
    rotate();
  }
  cout << "NO" << endl;
  return 0;
}