#include <iostream>
#include <algorithm>
#include <iomanip>
#include <vector>
#include <queue>
#include <set>
#include <map>

using namespace std;
typedef long long ll;

vector<int> A[100000];

bool all_0_row, all_1_row, all_0_col, all_1_col;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << setprecision(10) << fixed;
    int H, W;
    cin >> H >> W;
    for(int i = 0; i < H; i++){
        for(int j = 0; j < W; j++){
            char c;
            cin >> c;
            int a = c-'0';
            A[i].push_back(a);
        }
    }
    for(int i = 0; i < H; i++){
        int cnt = 0;
        for(int j = 0; j < W; j++){
            cnt += A[i][j];
        }
        if(cnt == W) all_1_row = true;
        if(cnt == 0) all_0_row = true;
    }

    for(int j = 0; j < W; j++){
        int cnt = 0;
        for(int i = 0; i < H; i++){
            cnt += A[i][j];
        }
        if(cnt == H) all_1_col = true;
        if(cnt == 0) all_0_col = true;
    }
    if(all_0_col && all_0_row) cout << "NO" << endl;
    else if(all_1_col && all_1_row) cout << "NO" << endl;
    else cout << "YES" << endl;
}