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

const int maxn = 1e3+5;

int val[maxn*maxn*2];

vector<pair<int, int>> g[maxn*maxn*2];
int good = 1;
void dfs(int x) {
    for(auto v: g[x]){
        if(val[v.first] == -1){
            val[v.first] = val[x]^v.second;
            dfs(v.first);
        }
        else{
            if(val[v.first] != (val[x]^v.second)){
                good = 0;
            }
        }
    }
}

bool reversal(int N, int M, vector<string> P){
    memset(val, -1, sizeof(val));
    for(int i = 0; i < N; i++){
        for(int j = 0; j < N; j++){
            g[M*i + j%M].push_back({i%M + M * j + M*N, P[i][j] == 'O'});
            g[i%M + M * j + M*N].push_back({M*i + j%M, P[i][j] == 'O'});

        }
    }
    for(int i = 0; i < M*N*2; i++){
        if(val[i] == -1){
            val[i] = 0;
            dfs(i);
        }
    }
    return good;
}

// int main() {
//     int N, M;
//     cin >> N >> M;
//     vector<string> P(N);
//     for(auto &v: P)cin >> v;
//     cout << reversal(N, M, P);
// }