Fox Ciel is playing a mobile puzzle game called "Two Dots". The basic levels are played on a board of size n × m cells, like this:

Each cell contains a dot that has some color. We will use different uppercase Latin characters to express different colors.

The key of this game is to find a cycle that contain dots of same color. Consider 4 blue dots on the picture forming a circle as an example. Formally, we call a sequence of dots d₁, d₂, ..., d_k a cycle if and only if it meets the following condition:

1. These k dots are different: if i ≠ j then d_i is different from d_j.
2. k is at least 4.
3. All dots belong to the same color.
4. For all 1 ≤ i ≤ k - 1: d_i and d_i + 1 are adjacent. Also, d_k and d₁ should also be adjacent. Cells x and y are called adjacent if they share an edge.

Determine if there exists a cycle on the field.

The first line contains two integers n and m (2 ≤ n, m ≤ 50): the number of rows and columns of the board.

Then n lines follow, each line contains a string consisting of m characters, expressing colors of dots in each line. Each character is an uppercase Latin letter.

Output "Yes" if there exists a cycle, and "No" otherwise.

In first sample test all 'A' form a cycle.

In second sample there is no such cycle.

The third sample is displayed on the picture above ('Y' = Yellow, 'B' = Blue, 'R' = Red).

#include<cstdio>

#include<cstdlib>

using namespace std;

const int N=105;

int n,m,ans,dir[4][2]={{0,1},{0,-1},{1,0},{-1,0}};

char mp[N][N];bool vis[N][N]={0};

void dfs(int x,int y,int px,int py,int step){

	vis[x][y]=1;

	for(int i=0;i<4;i++){

		int nx=x+dir[i][0];

		int ny=y+dir[i][1];

		if(nx<1||ny<1||nx>n||ny>m||mp[nx][ny]!=mp[x][y]) continue;

		if(!vis[nx][ny]) dfs(nx,ny,x,y,step+1);

		else{

			if((nx!=px||ny!=py)&&step>=4){puts("Yes");exit(0);}

		}

	}

}

inline void Init(){

	scanf("%d%d",&n,&m);

	for(int i=1;i<=n;i++) scanf("%s",mp[i]+1);

}

inline void Solve(){

	for(int i=1;i<=n;i++){

		for(int j=1;j<=m;j++){

			if(!vis[i][j]){

				dfs(i,j,0,0,1);

			}

		}

	}

	puts("No");

}

int main(){

	Init();

	Solve();

	return 0;

}