// need
#include <iostream>
#include <algorithm>
// data structure
#include <bitset>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>
#include <complex>
//#include <deque>
#include <valarray>
#include <unordered_map>
#include <unordered_set>
#include <array>
// etc
#include <cassert>
#include <cmath>
#include <functional>
#include <iomanip>
#include <chrono>
#include <random>
#include <numeric>
#include <fstream>

// input
#define INIT std::ios::sync_with_stdio(false);std::cin.tie(0);
#define VAR(type, ...)type __VA_ARGS__;MACRO_VAR_Scan(__VA_ARGS__);
template<typename T> void MACRO_VAR_Scan(T& t) { std::cin >> t; }
template<typename First, typename...Rest>void MACRO_VAR_Scan(First& first, Rest& ...rest) { std::cin >> first; MACRO_VAR_Scan(rest...); }
#define VEC_ROW(type, n, ...)std::vector<type> __VA_ARGS__;MACRO_VEC_ROW_Init(n, __VA_ARGS__); for(int w_=0; w_<n; ++w_){MACRO_VEC_ROW_Scan(w_, __VA_ARGS__);}
template<typename T> void MACRO_VEC_ROW_Init(int n, T& t) { t.resize(n); }
template<typename First, typename...Rest>void MACRO_VEC_ROW_Init(int n, First& first, Rest& ...rest) { first.resize(n); MACRO_VEC_ROW_Init(n, rest...); }
template<typename T> void MACRO_VEC_ROW_Scan(int p, T& t) { std::cin >> t[p]; }
template<typename First, typename...Rest>void MACRO_VEC_ROW_Scan(int p, First& first, Rest& ...rest) { std::cin >> first[p]; MACRO_VEC_ROW_Scan(p, rest...); }
#define VEC(type, c, n) std::vector<type> c(n);for(auto& i:c)std::cin>>i;
#define MAT(type, c, m, n) std::vector<std::vector<type>> c(m, std::vector<type>(n));for(auto& R:c)for(auto& w:R)std::cin>>w;
// output
template<typename T>void MACRO_OUT(const T t) { std::cout << t; }
template<typename First, typename...Rest>void MACRO_OUT(const First first, const Rest...rest) { std::cout << first << " "; MACRO_OUT(rest...); }
#define OUT(...) MACRO_OUT(__VA_ARGS__);
#define FOUT(n, dist) std::cout<<std::fixed<<std::setprecision(n)<<(dist);
#define SOUT(n, c, dist) std::cout<<std::setw(n)<<std::setfill(c)<<(dist);
#define SP std::cout<<" ";
#define TAB std::cout<<"\t";
#define BR std::cout<<"\n";
#define SPBR(w, n) std::cout<<(w + 1 == n ? '\n' : ' ');
#define ENDL std::cout<<std::endl;
#define FLUSH std::cout<<std::flush;
#define SHOW(dist) {std::cerr << #dist << "\t: " << (dist) << "\n";}
#define SHOWVECTOR(v) {std::cerr << #v << "\t: ";for(const auto& xxx : v){std::cerr << xxx << " ";}std::cerr << "\n";}
#define SHOWVECTOR2(v) {std::cerr << #v << "\t:\n";for(const auto& xxx : v){for(const auto& yyy : xxx){std::cerr << yyy << " ";}std::cerr << "\n";}}
#define SHOWQUEUE(a) {auto tmp(a);std::cerr << #a << "\t: ";while(!tmp.empty()){std::cerr << tmp.front() << " ";tmp.pop();}std::cerr << "\n";}
#define SHOWSTACK(a) {auto tmp(a);std::cerr << #a << "\t: ";while(!tmp.empty()){std::cerr << tmp.top() << " ";tmp.pop();}std::cerr << "\n";}
// utility
#define ALL(a) (a).begin(),(a).end()
#define FOR(w, a, n) for(int w=(a);w<(n);++w)
#define RFOR(w, a, n) for(int w=(n)-1;w>=(a);--w)
#define REP(w, n) for(int w=0;w<int(n);++w)
#define RREP(w, n) for(int w=int(n)-1;w>=0;--w)
#define IN(a, x, b) (a<=x && x<b)
template<class T> inline T CHMAX(T & a, const T b) { return a = (a < b) ? b : a; }
template<class T> inline T CHMIN(T& a, const T b) { return a = (a > b) ? b : a; }
// test
template<class T> using V = std::vector<T>;
template<class T> using VV = V<V<T>>;

template<typename S, typename T>
std::ostream& operator<<(std::ostream& os, std::pair<S, T> p) {
	os << "(" << p.first << ", " << p.second << ")"; return os;
}

// type/const
#define int ll
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using PAIR = std::pair<int, int>;
using PAIRLL = std::pair<ll, ll>;
constexpr int INFINT = (1 << 30) - 1;                    // 1.07x10^ 9
constexpr int INFINT_LIM = (1LL << 31) - 1;              // 2.15x10^ 9
constexpr ll INFLL = 1LL << 60;                          // 1.15x10^18
constexpr ll INFLL_LIM = (1LL << 62) - 1 + (1LL << 62);  // 9.22x10^18
constexpr double EPS = 1e-10;
constexpr int MOD = 998244353;
constexpr double PI = 3.141592653589793238462643383279;
template<class T, size_t N> void FILL(T(&a)[N], const T & val) { for (auto& x : a) x = val; }
template<class ARY, size_t N, size_t M, class T> void FILL(ARY(&a)[N][M], const T & val) { for (auto& b : a) FILL(b, val); }
template<class T> void FILL(std::vector<T> & a, const T & val) { for (auto& x : a) x = val; }
template<class ARY, class T> void FILL(std::vector<std::vector<ARY>> & a, const T & val) { for (auto& b : a) FILL(b, val); }
// ------------>8------------------------------------->8------------

namespace slow {
	struct Data {
		int y1, x1, y2, x2;
		bool f;
		Data() {}
		Data(int y1, int x1, int y2, int x2, bool f) : y1(y1), x1(x1), y2(y2), x2(x2), f(f) {}
		bool operator<(const Data& r) const {
			if (f != r.f) return f;
			return std::tie(y1, x1, y2, x2) < std::tie(r.y1, r.x1, r.y2, r.x2);
		}
	};
	std::map<Data, bool> map;
	bool slow(const VV<char>& a, int y1, int x1, int y2, int x2, bool rev = false) {
		Data d(y1, x1, y2, x2, rev);
		if (map.count(d)) return map[d];
		auto& res = map[d];

		OUT(y1)SP OUT(x1)SP OUT(y2)SP OUT(x2)BR;
		if (y1 + 1 == y2 && x1 + 1 == x2) return res = (a[y1][x1] == '1') ^ rev;
		FOR(i, y1 + 1, y2) {
			if (slow(a, y1, x1, i, x2, rev) && slow(a, i, x1, y2, x2, !rev)) return res = true;
			if (slow(a, y1, x1, i, x2, !rev) && slow(a, i, x1, y2, x2, rev)) return res = true;
		}
		FOR(j, x1 + 1, x2) {
			if (slow(a, y1, x1, y2, j, rev) && slow(a, y1, j, y2, x2, !rev)) return res = true;
			if (slow(a, y1, x1, y2, j, !rev) && slow(a, y1, j, y2, x2, rev)) return res = true;
		}
		return res = false;
	}
};

namespace experiment {
	std::set<VV<int>> as;
	void rec(VV<int> a, std::map<PAIR, PAIR> map) {
		if (map.empty()) {
			as.emplace(a);
			return;
		}
		auto it = map.begin();
		int y1, x1, y2, x2;
		std::tie(y1, x1) = it->first;
		std::tie(y2, x2) = it->second;
		map.erase(it);
		FOR(y, y1 + 1, y2) {
			auto tmap(map);
			if (y1 + 1 != y || x1 + 1 != x2) tmap[{y1, x1}] = { y, x2 };
			if (y + 1 != y2 || x1 + 1 != x2) tmap[{y, x1}] = { y2, x2 };
			FOR(i, y, y2) FOR(j, x1, x2) a[i][j] ^= 1;
			rec(a, tmap);
			FOR(i, y1, y2) FOR(j, x1, x2) a[i][j] ^= 1;
			rec(a, tmap);
			FOR(i, y1, y) FOR(j, x1, x2) a[i][j] ^= 1;
		}
		FOR(x, x1 + 1, x2) {
			auto tmap(map);
			if (y1 + 1 != y2 || x1 + 1 != x) tmap[{y1, x1}] = { y2, x };
			if (y1 + 1 != y2 || x + 1 != x2) tmap[{y1, x}] = { y2, x2 };
			FOR(i, y1, y2) FOR(j, x, x2) a[i][j] ^= 1;
			rec(a, tmap);
			FOR(i, y1, y2) FOR(j, x1, x2) a[i][j] ^= 1;
			rec(a, tmap);
			FOR(i, y1, y2) FOR(j, x1, x) a[i][j] ^= 1;
		}
	}
	std::set<VV<int>> calc(int h, int w) {
		as.clear();
		VV<int> a(h, V<int>(w, 0));
		std::map<PAIR, PAIR> map;
		map[{0, 0}] = { h, w };
		rec(a, map);
		return as;
	}
}

signed main() {
	INIT;

	VAR(int, h, w);
	MAT(char, a, h, w);

	std::set<int> rowset, colset;
	//V<int> row(h, -1), col(w, -1);
	REP(i, h) {
		int pre = a[i][0] - '0';
		REP(j, w) {
			if (pre != a[i][j] - '0') {
				pre = -1;
				break;
			}
		}
		//row[i] = pre;
		rowset.emplace(pre);
	}
	REP(j, w) {
		int pre = a[0][j] - '0';
		REP(i, h) {
			if (pre != a[i][j] - '0') {
				pre = -1;
				break;
			}
		}
		//col[j] = pre;
		colset.emplace(pre);
	}
	REP(k, 2) {
		if (rowset.count(k) && colset.count(k)) {
			OUT("NO")BR;
			return 0;
		}
	}
	OUT("YES")BR;

	//SHOW(slow::slow(a, 0, 0, h, w));

	//auto vs = experiment::calc(h, w);
	/*REP(bit, 1 << (h * w)) {
		VV<int> a(h, V<int>(w, 0));
		REP(i, h) REP(j, w) {
			int t = i * w + j;
			if (bit & 1 << t) a[i][j] = 1;
		}
		if (!vs.count(a)) {
			SHOWVECTOR2(a);
		}
	}*/
	//for (auto& v : vs) {
		//SHOWVECTOR2(v);
	//}

	return 0;
}