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

int main(){
    unsigned long N, M;
    cin >> N >> M;
    string s;
    unsigned long a{0};
    for(unsigned long i = 0; i < N; ++i){
        cin >> s;
        a += count(s.begin(), s.end(), 'o');
    }
    puts(a & 1 ? "NO" : "YES");
}