#include "bits/stdc++.h"

using namespace std;

void solve()
{
	int h, w;
	cin >> h >> w;
	vector<string> g(h);
	for (auto &l : g) cin >> l;
	reverse(g.begin(), g.end());
	int oc = 0, ec = 0;
	for (int i = 0; i < h; i++)
	{
		for (int j = 0; j < w; j++)
		{
			if (g[i][j] == 'o')
			{
				((i + j + 1) % 2 ? oc : ec) += 1;
			}
		}
	}
	cout << ((oc + ec + 1) % 2 ? "YES" : "NO") << endl;
}

int main()
{
	solve();
	//cout << "yui(*-v・)yui" << endl;
	return 0;
}