import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Main {
	public static void main(String[] args) throws Exception {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String[] sa = br.readLine().split(" ");
		int h = Integer.parseInt(sa[0]);
		int w = Integer.parseInt(sa[1]);
		char[][] a = new char[h][w];
		for (int i = 0; i < h; i++) {
			a[i] = br.readLine().toCharArray();
		}
		br.close();

		boolean[] h0 = new boolean[h];
		boolean[] h1 = new boolean[h];
		for (int i = 0; i < h; i++) {
			boolean f0 = true;
			boolean f1 = true;
			for (int j = 0; j < w; j++) {
				if (a[i][j] == '0') {
					f1 = false;
				} else {
					f0 = false;
				}
			}
			h0[i] = f0;
			h1[i] = f1;
		}

		boolean[] w0 = new boolean[w];
		boolean[] w1 = new boolean[w];
		for (int j = 0; j < w; j++) {
			boolean f0 = true;
			boolean f1 = true;
			for (int i = 0; i < h; i++) {
				if (a[i][j] == '0') {
					f1 = false;
				} else {
					f0 = false;
				}
			}
			w0[j] = f0;
			w1[j] = f1;
		}

		for (int i = 0; i < h; i++) {
			for (int j = 0; j < w; j++) {
				if (h0[i] && w0[j] || h1[i] && w1[j]) {
					System.out.println("NO");
					return;
				}
			}
		}
		System.out.println("YES");
	}
}