#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i, n) for(ll i = 0, i##_len = (n); i < i##_len; i++)
#define reps(i, s, n) for(ll i = (s), i##_len = (n); i < i##_len; i++)
#define rrep(i, n) for(ll i = (n) - 1; i >= 0; i--)
#define rreps(i, e, n) for(ll i = (n) - 1; i >= (e); i--)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define sz(x) ((ll)(x).size())
#define len(x) ((ll)(x).length())
#define endl "\n"
template<class T> void chmax(T &a, const T b){ a = max(a, b); }
template<class T> void chmin(T &a, const T b){ a = min(a, b); }
long long gcd(long long a, long long b) { return (a % b) ? gcd(b, a % b) : b; }
long long lcm(long long a, long long b) { return a / gcd(a, b) * b; }

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    // ifstream in("input.txt");
    // cin.rdbuf(in.rdbuf());
    ll h, w;
    cin >> h >> w;
    vector<string> s(h);
    rep(i, h) cin >> s[i];
    // {dy, dx}だけ並行移動すると仮定する全探索
    reps(dy, -h + 1, h) {
        reps(dx, -w + 1, w) {
            if ((dx == 0) && (dy == 0)) continue;
            vector<string> cs = s;
            bool f = true;
            ll cnt = 0;
            rrep(y, h) {
                rrep(x, w) {
                    if (cs[y][x] == '.') continue;
                    ll ny = y - dy;
                    ll nx = x - dx;
                    if ((ny < 0) || (nx < 0) || (ny >= h) || (nx >= w) || (cs[ny][nx] == '.')) {
                        f = false;
                        break;
                    }
                    cs[ny][nx] = '.';
                    cnt++;
                }
            }
            if (f && cnt) {
                cout << "YES" << endl;
                return 0;
            }
        }
    }
    cout << "NO" << endl;
    return 0;
}