#include <bits/stdc++.h>
#define db double
#define il inline
#define re register
#define ll long long
#define ui unsigned
#define ull ui ll
#define i128 __int128
#define pii pair<int, int>
#define fi first
#define se second
#define eb emplace_back
#define SZ(v) (int)v.size()
#define ALL(v) v.begin(), v.end()
#define mems(v, x) memset(v, x, sizeof(v))
#define memc(a, b) memcpy(a, b, sizeof(a))
#define FOR(i, L, R) for(re int i = (L); i <= (R); ++i)
#define ROF(i, R, L) for(re int i = (R); i >= (L); --i)
#define LS i << 1, l, mid
#define RS i << 1 | 1, mid + 1, r
#define popc(x) __builtin_popcount(x)
using namespace std;
#define N 20005
#define M 2019
int n, m;
il void WORK() {
  int xl = n, xr = 0, yl = m, yr = 0, cnt = 0;
  FOR(i, 1, n) {
    FOR(j, 1, m) {
      char c; cin >> c;
      if(c & 1) ++cnt, xl = min(xl, i), xr = max(xr, i), yl = min(yl, j), yr = max(yr, j);
    }
  }
  if(cnt == (xr - xl + 1) * (yr - yl + 1)) cout << "Yes\n";
  else cout << "No\n";
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0), cout.tie(0);
  while(cin >> n >> m) WORK();
  cerr << 1.0 * clock() / CLOCKS_PER_SEC;
  return 0;
}