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

struct dsu {
  public:
    dsu() : _n(0) {}
    dsu(int n) : _n(n), parent_or_size(n, -1) {}

    int merge(int a, int b) {
        assert(0 <= a && a < _n);
        assert(0 <= b && b < _n);
        int x = leader(a), y = leader(b);
        if (x == y) return x;
        if (-parent_or_size[x] < -parent_or_size[y]) std::swap(x, y);
        parent_or_size[x] += parent_or_size[y];
        parent_or_size[y] = x;
        return x;
    }

    bool same(int a, int b) {
        assert(0 <= a && a < _n);
        assert(0 <= b && b < _n);
        return leader(a) == leader(b);
    }

    int leader(int a) {
        assert(0 <= a && a < _n);
        if (parent_or_size[a] < 0) return a;
        return parent_or_size[a] = leader(parent_or_size[a]);
    }

    int size(int a) {
        assert(0 <= a && a < _n);
        return -parent_or_size[leader(a)];
    }

    std::vector<std::vector<int>> groups() {
        std::vector<int> leader_buf(_n), group_size(_n);
        for (int i = 0; i < _n; i++) {
            leader_buf[i] = leader(i);
            group_size[leader_buf[i]]++;
        }
        std::vector<std::vector<int>> result(_n);
        for (int i = 0; i < _n; i++) {
            result[i].reserve(group_size[i]);
        }
        for (int i = 0; i < _n; i++) {
            result[leader_buf[i]].push_back(i);
        }
        result.erase(
            std::remove_if(result.begin(), result.end(),
                           [&](const std::vector<int>& v) { return v.empty(); }),
            result.end());
        return result;
    }

  private:
    int _n;
    // root node: -1 * component size
    // otherwise: parent
    std::vector<int> parent_or_size;
};

int main(){
    int h, w;
    cin >> h >> w;
    vector<string> A(h);
    for(auto &&s:A)cin >> s;
    dsu uf(h * w);
    auto f = [&](int y, int x){return y * w + x;};
    auto g = [&](int v){return make_pair(v / w, v % w);};
    for(int y = 0; y < h; y++){
        for(int x = 0; x < w; x++){
            if(A[y][x] == '#')continue;
            if(x + 1 < w && A[y][x] == A[y][x + 1])uf.merge(f(y, x), f(y, x + 1));
            if(y + 1 < h && A[y][x] == A[y + 1][x])uf.merge(f(y, x), f(y + 1, x));
        }
    }
    auto G = uf.groups();
    int cnt = 0;
    vector<int> tar;
    for(auto &&vec:G){
        int y, x;
        tie(y, x) = g(vec[0]);
        cnt += (A[y][x] == '.');
        if(A[y][x] == '.')tar = vec;
    }
    if(cnt >= 2){
        cout << "NO" << endl;
        return 0;
    }
    vector<pair<int,int>> d={{-1,0},{0,-1},{1,0},{0,1}};
    vector<bool> used(h * w);
    function<bool(int,int,int,int,int)> dfs=[&](int y,int x,int s,int sy,int sx){
        if(y < 0 || x < 0 || y >= h || x >= w)return false;
        if(A[y][x] == '#')return false;
        if(used[f(y, x)] && y == sy && x == sx)return (count(used.begin(), used.end(), true) == tar.size());
        if(used[f(y, x)])return false;
        used[f(y, x)] = true;
        if(dfs(y + d[s].first, x + d[s].second, s, sy, sx))return true;
        if(dfs(y + d[(s + 1) % 4].first, x + d[(s + 1) % 4].second, (s + 1) % 4, sy, sx))return true;
        used[f(y, x)] = false;
        return false;
    };
    for(auto &&v:tar){
        int y, x;
        tie(y, x) = g(v);
        for(int i = 0; i < 4; i++){
            fill(used.begin(), used.end(), false);
            if(dfs(y, x, i, y, x)){
                cout << "YES" << endl;
                return 0;
            }
        }
    }
    cout << "NO" << endl;
}