#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

bool func(ll& even) {
	even--;
	return even >= 0;
}

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

	ll cnt = 0;
	ll all = 0;
	ll even = 0;
	REP(i, H) {
		string s;
		cin >> s;
		REP(j, W) if (s[j] == 'o') {
			cnt++;
			ll num = (H - 1 - i) + j + 1;
			all += num;
			if (num % 2 == 0)even++;
		}
	}
	//cout << all << " " << even << endl;
	bool res1 = all % 2 == 0
		? func(even)
		: cnt - even > 0;
	bool res2 = even % 2 == 0;
	cout << (res1&&res2 ? "NO" : "YES") << endl;
	return 0;
}