#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main() {
    int n, m;
    cin >> n >> m;
    vector<vector<char>> matrix(n, vector<char>(m));
    vector<vector<int>> dp(n+1, vector<int>(m+1, 0));

    // 读取矩阵
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < m; ++j) {
            cin >> matrix[i][j];
        }
    }

    // 动态规划更新dp数组
    for (int i = 1; i <= n; ++i) {
        for (int j = 1; j <= m; ++j) {
            if (matrix[i-1][j-1] == matrix[i-1][j-2] && matrix[i-1][j-1] == matrix[i-2][j-1]) {
                dp[i][j] = dp[i-1][j-1] + 1;
            } else {
                dp[i][j] = 1;
            }
        }
    }

    cout << dp[n][m] << endl;

    return 0;
}