#include <bits/stdc++.h>
using namespace std::literals::string_literals;
using i64 = std::int_fast64_t;
using std::cout;
using std::endl;
using std::cin;

template<typename T>
std::vector<T> make_v(size_t a){return std::vector<T>(a);}

template<typename T,typename... Ts>
auto make_v(size_t a,Ts... ts){
  return std::vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));
}

int main() {
	// input
	int h, w; scanf("%d%d", &h, &w);
	assert(1 <= h);
	assert(1 <= w);
	assert(h * w <= (int)1e5);
	
	std::vector<std::string> s(h);
	for(int i = 0; i < h; i++) {
		cin >> s[i];
		
		assert(s[i].size() == w);
		for(auto c: s[i]) assert(c == '1' or c == '0');
	}
	
	bool A = true, B = true;
	for(int i = 0; i < h; i++) {
		A &= (!all_of(begin(s[i]), end(s[i]), [](auto x) { return x == '0'; })
			and !all_of(begin(s[i]), end(s[i]), [](auto x) { return x == '1'; }));
	}
	for(int i = 0; i < w; i++) {
		int x = 0, y = 0;
		for(int j = 0; j < h; j++) {
			x += (s[j][i] == '0');
			y += (s[j][i] == '1');
		}
		B &= (x and y); 
	}
	
	if(A or B) printf("YES\n");
	else printf("NO\n");
	return 0;
}