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

int main(){
    unsigned long N, M;
    cin >> N >> M;
    string s;
    unsigned long a{0}, c{0};
    for(unsigned long i = 0; i < N; ++i){
        cin >> s;
        for(unsigned long j = 0; j < M; ++j){
            if(s[j] == 'o'){
                a += (N - i - 1) + (M - j - 1);
                c ^= 1;
            }
        }
    }
    puts(c & 1 ? "NO" : a & 1 ? "YES" : "NO");
}