//#define NDEBUG
#include <algorithm>
#include <cstddef>
#include <cstdint>
#include <iostream>
#include <vector>

namespace n91 {

  using i8 = std::int_fast8_t;
  using i32 = std::int_fast32_t;
  using i64 = std::int_fast64_t;
  using u8 = std::uint_fast8_t;
  using u32 = std::uint_fast32_t;
  using u64 = std::uint_fast64_t;
  using isize = std::ptrdiff_t;
  using usize = std::size_t;

  struct rep {
    struct itr {
      usize i;
      constexpr itr(const usize i) noexcept : i(i) {}
      void operator++() noexcept { ++i; }
      constexpr usize operator*() const noexcept { return i; }
      constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
    };
    const itr f, l;
    constexpr rep(const usize f, const usize l) noexcept
      : f(std::min(f, l)), l(l) {}
    constexpr auto begin() const noexcept { return f; }
    constexpr auto end() const noexcept { return l; }
  };
  struct revrep {
    struct itr {
      usize i;
      constexpr itr(const usize i) noexcept : i(i) {}
      void operator++() noexcept { --i; }
      constexpr usize operator*() const noexcept { return i; }
      constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
    };
    const itr f, l;
    constexpr revrep(const usize f, const usize l) noexcept
      : f(l - 1), l(std::min(f, l) - 1) {}
    constexpr auto begin() const noexcept { return f; }
    constexpr auto end() const noexcept { return l; }
  };
  template <class T> auto md_vec(const usize n, const T& value) {
    return std::vector<T>(n, value);
  }
  template <class... Args> auto md_vec(const usize n, Args... args) {
    return std::vector<decltype(md_vec(args...))>(n, md_vec(args...));
  }
  template <class T> constexpr T difference(const T& a, const T& b) noexcept {
    return a < b ? b - a : a - b;
  }
  template <class T> void chmin(T& a, const T& b) noexcept {
    if (b < a)
      a = b;
  }
  template <class T> void chmax(T& a, const T& b) noexcept {
    if (a < b)
      a = b;
  }
  template <class T> T scan() {
    T ret;
    std::cin >> ret;
    return ret;
  }

} // namespace n91

#include <algorithm>
#include <iostream>
#include <utility>

namespace n91 {

  void main_() {
    /*
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    //*/
    const usize h = scan<usize>();
    const usize w = scan<usize>();
    std::vector<std::string> a(h);
    for (auto& e : a) {
      std::cin >> e;
    }
    if (h == 1 && w == 1) {
      std::cout << (a[0][0] == '0' ? "NO" : "YES") << std::endl;
      return;
    }
    bool rf = false;
    for (const usize i : rep(0, h)) {
      usize cnt = 0;
      for (const usize j : rep(0, w)) {
        cnt += a[i][j] - '0';
      }
      if (cnt == 0 || cnt == w) {
        rf = true;
      }
    }
    bool cf = false;
    for (const usize i : rep(0, w)) {
      usize cnt = 0;
      for (const usize j : rep(0, h)) {
        cnt += a[j][i] - '0';
      }
      if (cnt == 0 || cnt == h) {
        cf = true;
      }
    }
    std::cout << (rf && cf ? "NO" : "YES") << std::endl;
  }

} // namespace n91

int main() {
  n91::main_();
  return 0;
}