#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define ld long double
#define pb push_back

ll n, m;
char a[100][100];
bool b[100][100];

bool bfs(ll i, ll j)
{
    queue<pair<ll, ll>> q;
    q.push({i, j});
    b[i][j] = 1;

    while (!q.empty())
    {
        ll f = q.front().first;
        ll s = q.front().second;

        q.pop();

        if (s < m - 1)
        {
            if (a[f][s + 1] == a[i][j])
            {
                if (!b[f][s + 1])
                {
                    b[f][s + 1] = 1;
                    q.push({f, s + 1});
                }
                else
                {
                    return 1;
                }
            }
        }

        if (f < n - 1)
        {
            if (a[f + 1][s] == a[i][j])
            {
                if (!b[f + 1][s])
                {
                    b[f + 1][s] = 1;
                    q.push({f + 1, s});
                }
                else
                {
                    return 1;
                }
            }
        }
    }

    return 0;
}

int main()
{
    cin >> n >> m;

    memset(a, 0, sizeof(a[0][0]) * 100 * 100);
    memset(b, 0, sizeof(b[0][0]) * 100 * 100);

    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < m; j++)
        {
            cin >> a[i][j];
        }
    }

    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < m; j++)
        {
            if (!b[i][j])
            {
                bool f = bfs(i, j);
                if (f)
                {
                    cout << "Yes" << endl;
                    return 0;
                }
            }
        }
    }

    cout << "No" << endl;

    return 0;
}