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#include<bits/stdc++.h>
#define FastIO      ios_base::sync_with_stdio(0);cin.tie(0),cout.tie(0)
#define pb          push_back
#define mp          make_pair
#define mem(x,i)    memset(x,i,sizeof(x))
#define ff          first
#define ss          second
#define all(x)      x.begin(),x.end()
#define fileout     freopen("output.txt","w",stdout)
#define filein      freopen("input.txt","r",stdin)
#define mod         1000000007
#define INF         1000000000
#define INF18       1e18
#define for1(i,n)   for( int i = 1 ; i<=n ; i++ )
#define for0(i,n)   for( int i = 0 ; i<n ; i++ )
typedef long long   ll;
const char nl = '\n';
#define MAX  1000
#define pii  pair< int , int >
using namespace std;

int fx[] = { 1, -1, 0, 0 };
int fy[] = { 0, 0, 1, -1 };
char cell[100][100];
int dis[100][100];
int vis[100][100];
map < pair<ll,ll> , pair<ll,ll> > parent;
int row, col;
bool found = false;

void DFS ( int sx, int sy, int cyclen )
{
    vis[sx][sy] = -1 ;

    for( ll k = 0 ; k<4 ; k++ )
    {
        ll tx = sx + fx[k];
        ll ty = sy + fy[k];

        if( tx >= 0 && tx<row && ty >= 0 && ty<col )
        {
            if( cell[tx][ty] == cell[sx][sy] )
            {
                if( vis[tx][ty] == 0 )
                {
                    parent[{tx,ty}] = make_pair(sx,sy);
                    DFS( tx,ty, cyclen+1 );
                }
                else if( parent[{sx,sy}] != make_pair(tx,ty) && vis[tx][ty] == -1   )
                {
                    if( cyclen>=4)
                    {
                        found = true;
                        break;
                    }
                }

            }
        }
    }

    vis[sx][sy] = 1;
}
int main()
{
    FastIO;
    cin>>row>>col;

    for( ll i = 0 ; i<row ; i++ )
    {
        for( ll j = 0; j<col ; j++ )
        {
            cin>>cell[i][j];
        }
    }
    for( ll i = 0 ; i<row ; i++ )
    {
        for( ll j = 0; j<col ; j++ )
        {
            if( vis[i][j]==0 )
            {
                DFS( i,j,1);
            }
            if( found )
            {
                cout<<"Yes"<<endl;
                return 0;
            }
        }
    }

    cout<<"No"<<endl;
    return 0;
}