import std.stdio, std.conv, std.string, std.array, std.range, std.algorithm, std.container;
import std.math, std.random, std.bigint, std.datetime, std.format;
void main(string[] args){ if(args.length > 1) if(args[1] == "-debug") DEBUG = 1; solve(); }
void log()(){ writeln(""); } void log(T, A ...)(T t, lazy A a){ if(DEBUG) write(t, " "), log(a); } bool DEBUG = 0; 
string read(){ static string[] ss; while(!ss.length) ss = readln.chomp.split; string res = ss[0]; ss.popFront; return res; }
T read(T)(){ return read.to!T; }
T[] read(T)(long n){ return n.iota.map!(_ => read!T).array; }
T[][] read(T)(long m, long n){ return m.iota.map!(_ => read!T(n)).array; }
// ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- //

void solve(){
	int n = read.to!int;
	
	bool[][] as;
	foreach(i; 0 .. n){
		as ~= readln.to!(char[]).map!(x => x == '#').array;
	}
	
	string ans = "YES";
	
	foreach(i; 0 .. n) foreach(j; 0 .. n){
		if(as[i][j]) continue;
		if(j - 1 < 0 || i + 2 >= n || j + 1 >= n){
			"NO".writeln;
			return;
		}
		if(as[i + 1][j - 1] || as[i + 1][j] || as[i + 1][j + 1] || as[i + 2][j]){
			"NO".writeln;
			return;
		}
		as[i][j] = 1;
		as[i + 1][j - 1] = 1;
		as[i + 1][j] = 1;
		as[i + 1][j + 1]  = 1;
		as[i + 2][j] = 1;
	}
	
	"YES".writeln;
	return;
	
}
