#include <iostream>
using namespace std;

const int kMAX_H = 60;
const int kMAX_W = 60;

string S[kMAX_H];
int color[kMAX_H][kMAX_W];
bool used[kMAX_H][kMAX_H];

int H, W, red, blue;

int dr[] = {1, 0, -1, 0},
    dc[] = {0, 1, 0, -1};

bool DFS(int row, int col, int c) {
    used[row][col] = true;
    color[row][col] = c;
    if (c == 1) red++;
    else blue--;

    for (int i = 0; i < 4; i++) {
        int nr = row + dr[i], nc = col + dc[i];
        if (0 <= nr && nr < H && 0 <= nc && nc < W && !used[nr][nc] && !DFS(nr, nc, -c)) {
            return false;
        }
    }

    return true;
}

void Solve() {
    for (int i = 0; i < H; i++) {
        for (int j = 0; j < W; j++) {
            if (S[i][j] == '.') used[i][j] = true;
        }
    }

    for (int i = 0; i < H; i++) {
        for (int j = 0; j < W; j++) {
            if (!used[i][j] && !DFS(i, j, 1)) {
                cout << "NO" << endl;
                return;
            }
        }
    }

    if ((red + blue) % 2 == 0) {
        cout << "YES" << endl;
    } else {
        cout << "NO" << endl;
    }
}

int main() {
    cin >> H >> W;

    for (int i = 0; i < H; i++) {
        cin >> S[i];
    }

    Solve();

    return 0;
}