#include <iostream>
#include <sstream>
#include <string>
#include <vector>
#include <functional>
#include <tuple>
#include <climits>
#include <algorithm>
#include <queue>
#include <unordered_map>
#include <unordered_set>
#include <set>
#include <iomanip>

using namespace std;
int main()
{
    int H, W;
    cin >> H >> W;
    vector<string> tile(H);
    set<tuple<int, int>> black;
    enum {
        width = 0,
        height = 1
    };
    for(int i=0; i<H; i++) {
        cin >> tile[i];
        for(int j=0; j<tile[i].size(); j++) {
            if(tile[i][j] == '.') continue;
            black.insert(make_tuple(j, i));
        }
    }
    if(black.size() % 2 == 1 || black.size()==0) {
        cout << "NO" << endl;
        return 0;
    }
    for(int w=-W+1; w<W; w++) {
        for(int h=-H+1; h<H; h++) {
            if(w == 0 && h == 0) continue;
            set<tuple<int, int>> b(black);
            for(const auto& t : b) {
                int x = get<width>(t)+w;
                int y = get<height>(t)+h;
                if(b.count(make_tuple(x, y)) == 0) break;
                b.erase(make_tuple(x, y));
            }
            if(b.size() == black.size()/2) {
                cout << "YES" << endl;
                return 0;
            }
        }
    }
    cout << "NO" << endl;
}