#include <iostream>
#include <vector>
#include <algorithm>
#include <iomanip>
#include <string>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <climits>
#include <cassert>
#include <cstdint>
#include <numeric>
#include <bitset>
#include <functional>

using namespace std;

using ll =  long long;
using Pll = pair<ll, ll>;
using Pii = pair<int, int>;

constexpr ll MOD = 1000000007;
constexpr long double EPS = 1e-10;
constexpr int dyx[4][2] = {
    { 0, 1}, {-1, 0}, {0,-1}, {1, 0}
};

int main() {
    ios::sync_with_stdio(false); cin.tie(nullptr);
    int h, w;
    cin >> h >> w;
    vector<vector<bool>> has_in_row(h, vector<bool>(2, false)), has_in_column(w, vector<bool>(2, false));

    string s;
    for(int i=0;i<h;++i){
        cin >> s;
        for(int j=0;j<w;++j) {
            has_in_row[i][s[j]-'0'] = true;
            has_in_column[j][s[j]-'0'] = true;
        }
    }

    bool is_ok_row = true, is_ok_column = true;
    if(w != 1) {
        for(int i=0;i<h;++i){
            if(!has_in_row[i][0] || !has_in_row[i][1]) {
                is_ok_row = false;
                break;
            }
        }
    }
    if(h != 1) {
        for(int i=0;i<w;++i){
            if(!has_in_column[i][0] || !has_in_column[i][1]) {
                is_ok_column = false;
                break;
            }
        }
    }

    if(is_ok_column || is_ok_row) {
        cout << "YES" << endl;
    } else {
        cout << "NO" << endl;
    }
}