import std.stdio, std.string, std.conv, std.algorithm, std.numeric;
import std.range, std.array, std.math, std.typecons, std.container, core.bitop;


void main() {
    int h, w;
    scan(h, w);

    auto map = new int[][](h, w);
    int kuro = h*w;

    foreach (i ; 0 .. h) {
        string s = readln.chomp;
        foreach (int j, ch; s) {
            if (ch == '.') {
                map[i][j] = 1;
                kuro--;
            }
        }
    }

    if (kuro==0){
        writeln("NO");
        return;
    }

    foreach (x ; 0 .. h) {
        foreach (y ; 0 .. w) {
            if (x + y == 0) continue;

            bool ok = 1;
            auto m = new int[][](h, w);
            iota(h).each!(i => m[i] = map[i].dup);

            foreach (i ; 0 .. h) {
                foreach (j ; 0 .. w) {
                    if (m[i][j]) continue;

                    m[i][j] = 2;

                    if (i + x >= h || j + y >= w || m[i+x][j+y]) {
                        ok = 0;
                    }
                    else {
                        m[i + x][j + y] = 3;
                    }
                }
            }

            if (ok) {
                debug {
                    writefln("%(%(%s %)\n%)", m);
                    writeln(x, " ", y);
                }
                writeln("YES");
                return;
            }
        }
    }

    writeln("NO");
}



void scan(T...)(ref T args) {
    string[] line = readln.split;
    foreach (ref arg; args) {
        arg = line.front.to!(typeof(arg));
        line.popFront();
    }
    assert(line.empty);
}



void fillAll(R, T)(ref R arr, T value) {
    static if (is(typeof(arr[] = value))) {
        arr[] = value;
    }
    else {
        foreach (ref e; arr) {
            fillAll(e, value);
        }
    }
}