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

#define reps(i,a,b) for(int i=(a);i<(b);++i)
#define rep(i,n)   reps(i,0,n)
#define all(x) (x).begin(),(x).end()
#define INF (1000000000)
#define MOD (1000000007)
#define PI (acos(-1))

int main(){
  int H,W;
  cin >> H >> W;
  char c[H][W];

  int num=0;
  rep(i,H){
    rep(j,W){
      cin >> c[i][j];
      if(c[i][j] == 'o')num++;
    }
  }

  int cnt=0;
  rep(k,400){
    rep(i,H){
      rep(j,W){

        if(c[i][j]=='o'){

          if(i != H-1){
            if(c[i+1][j] == '-'){
              c[i][j] = '-';
              c[i+1][j] = 'o';
              cnt++;
              continue;
            }
          }

          if(j!=0){
            if(c[i][j-1] == '-'){
              c[i][j] = '-';
              c[i][j-1] = 'o';
              cnt++;
              continue;
            }
          }

        }
      }
    }
  }

  /*rep(i,H){
    rep(j,W){
      cout << c[i][j];
    }
    cout << endl;
  }*/

  if((num+cnt)%2==0){
    cout << "YES" << endl;
  }else{
    cout << "NO" << endl;
  }
}