//
// Created by zeronosu77108 on Jan 15, 2021.
//
#include <iostream>
#include <iomanip>
#include <vector>
#include <utility>
#include <map>
#include <unordered_map>
#include <unordered_set>
#include <algorithm>
#include <queue>
#include <cmath>
#include <numeric>
#include <set>
#include <complex>
#include <optional>
#include <climits>

using namespace std;
struct aaa{aaa(){cin.tie(nullptr); ios::sync_with_stdio(false); cout<<fixed<<setprecision(20);};}aaa;
template <class T>ostream &operator<<(ostream &o,const vector<T>&v){o<<"{";for(int i=0;i<(int)v.size();i++)o<<(i>0?", ":"")<<v[i];o<<"}";return o;}
#define debug(v) {cerr<<"\033[1;36m[debug]\033[m "<<#v<<" : "<<(v)<<endl;}

int main() {
    int h, w;
    cin >> h >> w;

    vector<string> s(h);
    for (int i=0; i<h; i++) cin >> s[i];

    for (int dy=0; dy<h; dy++) {
        for (int dx=0; dx<w; dx++) {
            if (dy==0 && dx==0) continue;
            vector used(h, vector(w, false));

            bool f = true;
            for (int i=0; i<h; i++) {
                for (int j=0; j<w; j++) {
                    if (s[i][j] == '.') continue;
                    if (used[i][j]) continue;
                    used[i][j] = true;

                    if (h<=i+dy || w<=j+dx) {f=false; break; }
                    if (s[i+dy][j+dx] == '.') {f=false; break;}
                    used[i+dy][j+dx] = true;
                }
                if (!f) break;
            }

            if (f) {
                cout << "YES" << endl;
                return 0;
            }
        }
    }

     cout << "NO" << endl;
}