#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using PII = pair<ll, ll>;
#define FOR(i, a, n) for (ll i = (ll)a; i < (ll)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define ALL(x) x.begin(), x.end()
template<typename T> void chmin(T &a, const T &b) { a = min(a, b); }
template<typename T> void chmax(T &a, const T &b) { a = max(a, b); }
struct FastIO {FastIO() { cin.tie(0); ios::sync_with_stdio(0); }}fastiofastio;
#ifdef DEBUG_ 
#include "../program_contest_library/memo/dump.hpp"
#else
#define dump(...)
#endif
const ll INF = 1LL<<60;

int main(void) {
    ll h, w;
    cin >> h >> w;
    vector<string> s(h);
    REP(i, h) cin >> s[i];

    bool f_all0 = false, f_all1 = false;
    REP(i, h) {
        ll cnt0 = 0, cnt1 = 0;
        REP(j, w) {
           if(s[i][j] == '0') cnt0++;
           else cnt1++; 
        }
        if(cnt0 == w) f_all0 = true;
        if(cnt1 == w) f_all1 = true;
    }

    bool g_all0 = false, g_all1 = false;
    REP(i, w) {
        ll cnt0 = 0, cnt1 = 0;
        REP(j, h) {
           if(s[j][i] == '0') cnt0++;
           else cnt1++; 
        }
        if(cnt0 == h) g_all0 = true;
        if(cnt1 == h) g_all1 = true;
    }

    if((f_all0 && g_all0) || (f_all1 && g_all1)) cout << "NO" << endl;
    else cout << "YES" << endl;

    return 0;
}