#include <bits/stdc++.h>
using namespace std;
int n, m;
char grid[55][55];
char vis[55][55];
int di[] = {0, 1, -1, 0};
int dj[] = {1, 0, 0, -1};
bool dfs(int pi, int pj, char c, int li = -1, int lj = -1) {
  if (vis[pi][pj]) return true;
  vis[pi][pj] = true;
  for (int d = 0; d < 4; d++) {
    int ni = pi + di[d];
    int nj = pj + dj[d];
    if (ni == li && nj == lj) continue;
    if (ni < 0 || ni >= n || nj < 0 || nj >= m) continue;
    if (grid[ni][nj] != c) continue;
    if (dfs(ni, nj, c, pi, pj)) return true;
  }
  return false;
}
int main() {
  cin >> n >> m;
  for (int i = 0; i < n; i++) {
    cin >> grid[i];
  }
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < m; j++) {
      if (vis[i][j] == false) {
        if (dfs(i, j, grid[i][j])) {
          cout << "Yes" << endl;
          return 0;
        }
      }
    }
  }
  cout << "No" << endl;
  return 0;
}
