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

#define EPS (1e-7)
#define INF (1e9)
#define PI (acos(-1))
//const ll mod = 1000000007;
int H, W;
string field[205];

int main() {
    //cout.precision(10);
    cin.tie(0);
    ios::sync_with_stdio(false);
    cin >> H >> W;
    int N = 0;
    int sum = 0;
    for(int h = 1; h <= H; h++) {
        cin >> field[h];
        field[h] = "#" + field[h];
        for(int w = 1; w <= W; w++) {
            if(field[h][w] == 'o') {
                N++;
                sum += h + w;
            }
        }
    }
    if(N % 2 == 0) {
        if((N % 4 == 0) xor (sum % 2 == 1)) cout << "YES" << endl;
        else cout << "NO" << endl;
        return 0;
    }
    N--;
    for(int h = 1; h <= H; h++) {
        for(int w = 1; w <= W; w++) {
            if(field[h][w] != 'o') continue;
            int now = sum - h - w;
            if((N % 4 == 0) xor (now % 2 == 1)) {
                cout << "NO" << endl;
                return 0;
            }
        }
    }
    cout << "YES" << endl;
    return 0;
}