1 /*
 2     DFS：每个点四处寻找，判断是否与前面的颜色相同，当走到已走过的表示成一个环
 3 */
 4 #include <cstdio>
 5 #include <iostream>
 6 #include <cstring>
 7 #include <string>
 8 #include <map>
 9 #include <algorithm>
10 #include <vector>
11 #include <set>
12 #include <cmath>
13 using namespace std;
14
15 const int MAXN = 1e6 + 10;
16 const int INF = 0x3f3f3f3f;
17 int dx[4] = {1, -1, 0, 0};
18 int dy[4] = {0, 0, 1, -1};
19 char a[55][55];
20 int used[55][55];
21 int n, m;
22
23 bool DFS(int x, int y, int px, int py, char ch)
24 {
25     used[x][y] = 1;
26     for (int i=0; i<=4-1; ++i)
27     {
28         int tx = x + dx[i];
29         int ty = y + dy[i];
30         if (tx == px && ty == py)   continue;
31         if (tx >= 0 && tx <= n-1 && ty >= 0 && ty <=m-1 && a[tx][ty] == ch)
32         {
33             if (used[tx][ty])   return true;
34             if (DFS (tx, ty, x, y, ch)) return true;
35         }
36     }
37
38     return false;
39 }
40
41 int main(void)
42 {
43     //freopen ("B.in", "r", stdin);
44
45     while (cin >> n >> m)
46     {
47         memset (used, 0, sizeof (used));
48         for (int i=0; i<=n-1; ++i)
49         {
50             scanf ("%s", &a[i]);
51         }
52
53         bool flag = false;
54         for (int i=0; i<=n-1; ++i)
55         {
56             for (int j=0; j<=m-1; ++j)
57             {
58                 if (!used[i][j])
59                 {
60                     if (DFS (i, j, -1, -1, a[i][j]))
61                     {
62                         puts ("Yes");   flag = true;    break;
63                     }
64                 }
65             }
66             if (flag)   break;
67         }
68
69         if (!flag)  puts ("No");
70     }
71
72     return 0;
73 }