510B_FoxAndTwoDots

#include <bits/stdc++.h>

using namespace std;

char a[55][55];
int x, y, n, m;
bool found = false, visited[55][55];
string s;

void Visit(int u, int v) {
    visited[u][v] = true;

    if (!found) {
/*
        if (a[u-1][v] == a[u][v])
            if (visited[u-1][v])
            {
                found = true;
                return;
            } else Visit(u-1, v);
*/
        if (a[u][v+1] == a[u][v])
            if (visited[u][v+1])
            {
                found = true;
                return;
            } else Visit(u, v+1);

        if (a[u+1][v] == a[u][v])
            if (visited[u+1][v])
            {
                found = true;
                return;
            } else Visit(u+1, v);
/*
        if (a[u][v-1] == a[u][v])
            if (visited[u][v-1])
            {
                found = true;
                return;
            }  else Visit(u, v-1);
*/
    }
}

int main() {
    #ifndef ONLINE_JUDGE
        freopen("cf510b.inp", "r", stdin);
    #endif // ONLINE_JUDGE

    scanf("%d%d", &n, &m); getline(cin, s);
    for (int i=1; i<=n; ++i)
    {
        getline(cin, s);
        for (int j=0; j<s.size(); ++j) a[i][j+1] = s[j];
    }

    for (int i=0; i<=n+1; ++i) a[i][0] = a[i][m+1] = '0';
    for (int i=0; i<=m+1; ++i) a[0][i] = a[n+1][i] = '0';
    memset(visited, false, sizeof(visited));

    for (int i=1; i<=n; ++i)
    {
        for (int j=1; j<=m; ++j)
        {
            if (a[i][j] != '0' && !visited[i][j]) Visit(i, j);
            if (found) break;
        }

        if (found) break;
    }

    if (!found) printf("No\n"); else printf("Yes\n");

    return 0;
}