codeforces510B

#include <bits/stdc++.h>
using namespace std;
typedef int ll;
inline ll read()
{
    ll s=0;
    bool f=0;
    char ch=‘ ‘;
    while(!isdigit(ch))
    {
        f|=(ch==‘-‘); ch=getchar();
    }
    while(isdigit(ch))
    {
        s=(s<<3)+(s<<1)+(ch^48); ch=getchar();
    }
    return (f)?(-s):(s);
}
#define R(x) x=read()
inline void write(ll x)
{
    if(x<0)
    {
        putchar(‘-‘); x=-x;
    }
    if(x<10)
    {
        putchar(x+‘0‘); return;
    }
    write(x/10);
    putchar((x%10)+‘0‘);
    return;
}
#define W(x) write(x),putchar(‘ ‘)
#define Wl(x) write(x),putchar(‘\n‘)
const int N=55;
const int dx[]={-1,1,0,0},dy[]={0,0,-1,1};
int n,m,SX,SY;
char Map[N][N];
bool Arr[N][N];
int Ges[N][N];
inline bool dfs(int x,int y)
{
    int i;
    Arr[x][y]=1;
    for(i=0;i<4;i++)
    {
        int xx=x+dx[i],yy=y+dy[i];
        if(xx<1||xx>n||yy<1||yy>m) continue;
        if(Map[xx][yy]==Map[x][y])
        {
            if(!Ges[xx][yy])
            {
                Ges[xx][yy]=Ges[x][y]+1;
                if(dfs(xx,yy)) return true;
                Ges[xx][yy]=0;
            }
            else
            {
                if(Ges[x][y]-Ges[xx][yy]+1>=4) return true;
            }
        }
    }
    return false;
}
int main()
{
    int i,j;
    R(n); R(m);
    for(i=1;i<=n;i++)
    {
        scanf("%s",Map[i]+1);
    }
    for(i=1;i<=n;i++)
    {
        for(j=1;j<=m;j++) if(!Arr[i][j])
        {
            Ges[i][j]=1;
            if(dfs(i,j)) return 0*puts("Yes");
        }
    }
    puts("No");
    return 0;
}
/*
input
3 4
AAAA
ABCA
AAAA
output
Yes

input
3 4
AAAA
ABCA
AADA
output
No

input
4 4
YYYR
BYBY
BBBY
BBBY
output
Yes

input
7 6
AAAAAB
ABBBAB
ABAAAB
ABABBB
ABAAAB
ABBBAB
AAAAAB
output
Yes

input
2 13
ABCDEFGHIJKLM
NOPQRSTUVWXYZ
output
No
*/