#include <iostream>
#include <vector>
#include <string>
using namespace std;
#define REP(i, N) for(int i=0;i<(N);++i)

int H, W;
string S[51];

bool canPaint(int di, int dj) {
    vector<vector<bool>> painted(H, vector<bool>(W, false));
    bool is_white_board = true;

    for (int i = 0; i < H; ++i) {
        for (int j = 0; j < W; ++j) {
            if (S[i][j] == '.' || painted[i][j]) continue;

            if (i+di < 0 || H <= i+di || j+dj < 0 || W <= j+dj) return false;
            if (S[i+di][j+dj] == '.' || painted[i+di][j+dj]) return false;

            painted[i][j] = true;
            painted[i+di][j+dj] = true;
            is_white_board = false;
        }
    }

    return !is_white_board;
}

int main() {
    cin >> H >> W;
    REP(i, H) cin >> S[i];

    bool can_paint = false;

    for (int i = 0; i < H; ++i) {
        for (int j = -W+1; j < W; ++j) {
            if (i == 0 && j == 0) continue;
            if (canPaint(i, j)) can_paint = true;
        }
    }

    if (can_paint) {
        cout << "YES" << endl;
    } else {
        cout << "NO" << endl;
    }
}