import core.thread;
import std.conv, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.container, std.math, std.range, std.regex;

//	Input
class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { tokens = readln.split; if (tokens.empty && stdin.eof) throw new EOFException; } auto token = tokens[0]; tokens.popFront; return token; }
int readInt() { return to!int(readToken); }
long readLong() { return to!long(readToken); }
real readReal() { return to!real(readToken); }

//	chmin/chmax
void chmin(T)(ref T t, in T f) { if (t > f) t = f; }
void chmax(T)(ref T t, in T f) { if (t < f) t = f; }

//	Pair
struct Pair(S, T) {
	S x; T y;
	int opCmp(    const Pair p) const { return (x < p.x) ? -1 : (x > p.x) ? +1 : (y < p.y) ? -1 : (y > p.y) ? +1 : 0; }
	int opCmp(ref const Pair p) const { return (x < p.x) ? -1 : (x > p.x) ? +1 : (y < p.y) ? -1 : (y > p.y) ? +1 : 0; }
	string toString() const { return "(" ~ to!string(x) ~ ", " ~ to!string(y) ~ ")"; }
}
auto pair(S, T)(inout(S) x, inout(T) y) { return Pair!(S, T)(x, y); }

//	Array
int binarySearch(T)(in T[] as, in bool delegate(T) test) { int low = -1, upp = as.length; for (; low + 1 < upp; ) { int mid = (low + upp) >> 1; (test(as[mid]) ? low : upp) = mid; } return upp; }
int lowerBound(T)(in T[] as, in T val) { return as.binarySearch((T a) { return (a <  val); }); }
int upperBound(T)(in T[] as, in T val) { return as.binarySearch((T a) { return (a <= val); }); }
T[] unique(T)(in T[] as) { T[] bs; foreach (a; as) if (bs.empty || bs[$ - 1] != a) bs ~= a; return bs; }


int M, N;
string[] A;

bool solve() {
	foreach (rot; 0 .. 4) {
		int xMin = int.max, yMin = int.max;
		int xMax = int.min, yMax = int.min;
		int cnt;
		foreach (x; 0 .. M) foreach (y; 0 .. N) if (A[x][y] == '.') {
			chmin(xMin, x);
			chmin(yMin, y);
			chmax(xMax, x);
			chmax(yMax, y);
			++cnt;
		}
debug{
writeln(xMin," ",xMax," ",yMin," ",yMax);
}
		if (xMin == xMax || yMin == yMax) {
			return false;
		}
		if (cnt != 2 * ((xMax - xMin) + (yMax - yMin))) {
			return false;
		}
		{
			bool ok = true;
			foreach (x; xMin .. xMax + 1) {
				ok = ok && (A[x][yMin] == '.');
				ok = ok && (A[x][yMax] == '.');
			}
			foreach (y; yMin .. yMax + 1) {
				ok = ok && (A[xMin][y] == '.');
				ok = ok && (A[xMax][y] == '.');
			}
			if (ok) {
				return true;
			}
		}
		foreach (sx; xMin + 1 .. xMax) foreach (sy; yMin + 1 .. yMax) {
			bool ok = true;
			foreach (y; yMin .. sy + 1) {
				ok = ok && (A[sx][y] == '.');
			}
			foreach (x; sx .. xMax + 1) {
				ok = ok && (A[x][yMin] == '.');
			}
			foreach (y; yMin .. yMax + 1) {
				ok = ok && (A[xMax][y] == '.');
			}
			foreach (x; xMin .. xMax + 1) {
				ok = ok && (A[x][yMax] == '.');
			}
			foreach (y; sy .. yMax + 1) {
				ok = ok && (A[xMin][y] == '.');
			}
			foreach (x; xMin .. sx + 1) {
				ok = ok && (A[x][sy] == '.');
			}
			if (ok) {
				return true;
			}
		}
		auto AA = A.dup;
		swap(M, N);
		A = new string[M];
		foreach (x; 0 .. M) foreach (y; 0 .. N) {
			A[x] ~= AA[N - 1 - y][x];
		}
	}
	return false;
}

void main(string[] args) {
	try {
	for (; ; ) {
		M = readInt;
		N = readInt;
		A = new string[M];
		foreach (x; 0 .. M) {
			A[x] = readToken;
		}
		
		const ans = solve;
		writeln(ans ? "YES" : "NO");
		
	}
	} catch (EOFException) {}
}