#include<bits/stdc++.h>
using namespace std;
using Int = long long;
template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;}
template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;}

//INSERT ABOVE HERE
const Int n=6;
const Int s=1<<n;
Int dp[s];
Int dfs(Int b){
  Int &res=dp[b];
  if(~res) return res;
  res=0;
  for(Int i=0;i<n;i++)
    if((b>>i)&1) res|=!dfs(b^(1<<i));
  for(Int i=1;i<n;i++){
    if((~b>>i)&1) continue;
    if((b>>(i-1))&1) continue;
    res|=!dfs(b^(1<<i)^(1<<(i-1)));
  }
  return res;
}

signed main(){
  /*
  memset(dp,-1,sizeof(dp));
  for(Int b=0;b<s;b++)
    cout<<bitset<n>(b)<<":"<<dfs(b)<<endl;  
  */
  Int h,w;
  cin>>h>>w;
  vector<string> st(h);
  for(Int i=0;i<h;i++) cin>>st[i];

  Int cnt[2]={};
  for(Int i=0;i<h;i++){
    for(Int j=0;j<w;j++){
      if(st[i][j]=='-') continue;
      cnt[(i+j)&1]++;
    }
  }
  cnt[0]%=3;
  cnt[1]%=3;
  cout<<(cnt[0]==cnt[1]?"YES":"NO")<<endl;
  return 0;
}