#include <bits/stdc++.h>
using namespace std;

int main(){
    int H, W;
    cin >> H >> W;
    vector<string> S(H);
    for(int i=0; i<H; i++) cin >> S[i];
    bool ok1 = true, ok2 = true;
    for(int i=0; i<H; i++){
        bitset<2> found;
        for(int j=0; j<W; j++) found[S[i][j]-'0'] = 1;
        ok1 &= found.all();
    }
    for(int j=0; j<W; j++){
        bitset<2> found;
        for(int i=0; i<H; i++) found[S[i][j]-'0'] = 1;
        ok2 &= found.all();
    }
    bool ok = (ok1 || ok2);
    cout << (ok ? "YES" : "NO") << endl;
    return 0;
}