/* 1760 */

 #include <cstdio>

 #include <cstring>

 #include <cstdlib>

 #define MAXN 55

 char map[MAXN][MAXN];

 int n, m;

 int cal_SG() {

     int i, j, k, r, p;

     for (i=; i<n-; ++i) {

         for (j=; j<m-; ++j) {

             if (map[i][j]=='' && map[i][j+]=='' && map[i+][j]=='' && map[i+][j+]=='') {

                 map[i][j] = map[i][j+] = map[i+][j] = map[i+][j+] = '';

                 k = cal_SG();

                 map[i][j] = map[i][j+] = map[i+][j] = map[i+][j+] = '';

                 if (k == )

                     return ;

             }

         }

     }

     return ;

 }

 int main() {

     int i, j, k;

     #ifndef ONLINE_JUDGE

         freopen("data.in", "r", stdin);

     #endif

     while (scanf("%d %d", &n, &m) != EOF) {

         for (i=; i<n; ++i)

             scanf("%s", map[i]);

         if (cal_SG() == )

             puts("No");

         else

             puts("Yes");

     }

     return ;

 }