#include<bits/stdc++.h>
#define PI 3.141592653589
#define ll long long
using namespace std;

template<typename T_char>
T_char ToUpper(T_char cX){return toupper(cX);}

int  main(){
  int h, w;
  cin >> h >> w;
  char s[h*w];
  for(int i=0; i<h*w; ++i) cin >> s[i];
  
  int cnt = 0, cnt1=0;
  for(int i=0; i<h*w; ++i){
    if(s[i]=='#') ++cnt;
    if(s[i]=='.') ++cnt1;
  }
  if(cnt%2==0 && cnt1%2==0) cout << "YES" << endl;
  else cout << "NO" << endl;
  return 0;
}