#include"bits/stdc++.h"

using namespace std;
using ll = long long;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;

#define FOR(k,m,n) for(ll (k)=(m);(k)<(n);(k)++)
#define REP(i,n) FOR((i),0,(n))
#define WAITING(str) int str;std::cin>>str;
#define DEBUGING(str) cout<< #str << " " str<<endl

constexpr int INF = (1 << 30);
constexpr ll INFL = (1ll << 60);
constexpr ll MOD = 1000000007;// 10^9+7



int main()
{
	int H, W;
	cin >> H >> W;

	int cnt = 0;
	int all = 0;
	int even = 0;
	REP(i, H) {
		string s;
		cin >> s;
		REP(j, W) if (s[j] == 'o') {
			cnt++;
			int num = (H - 1 - i) + j + 1;
			all += num;
			if (num % 2 == 0)even++;
		}
	}
	//cout << all << " " << even << endl;
	bool res1 = all % 2 == 0
		? even > 0
		: cnt - even > 0;
	bool res2 = (even - (all % 2 == 0 ? 1 : 0)) % 2 == 0;

	bool res = !(res1 && !res2);

	cout << (res ? "NO" : "YES") << endl;
	return 0;
}