#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);
	std::vector<std::string> s(h);
	for(int i = 0; i < h; i++) cin >> s[i];
	
	// solve
	bool X = true, Y = true;
	for(int loop = 0; loop < 2; loop++) {
		for(int i = 0; i < h; i++) {
			int x = 0, y = 0;
			for(int j = 0; j < w; j++) {
				if(loop) std::swap(i, j);
				x += (s[i][j] == '0');
				y += (s[i][j] == '1');
				if(loop) std::swap(i, j);
			}
			
			X &= (x and y);
		}
		std::swap(h, w);
		std::swap(X, Y);
	}
	
	if(X or Y) printf("YES\n");
	else printf("NO\n");
	return 0;
}