#include <iostream>

using namespace std;

const int MAXN = 1005;

char c[MAXN][MAXN];

int n, m, dx[] = {0, 0, -1, 1}, dy[] = {1, -1, 0, 0};

int main() {

    cin >> n >> m;

    char mx = 'A', ch = 'A';

    for (int i = 1; i <= n; ++i) {

        for (int j = 1; j <= m; ++j) {

            cin >> c[i][j];

            mx = max(mx, c[i][j]);

        }

    }

    for (int i = 1; i <= n; ++i) {

        for (int j = 1; j <= m; ++j) {

            if (c[i][j] == mx) {

                for (int k = 0; k < 4; ++k) {

                    int x = i + dx[k], y = j + dy[k];

                    if (x >= 1 && x <= n && y >= 1 && y <= m && c[x][y] != '#') {

                        ch = max(ch, c[x][y]);

                    }

                }

            }

        }

    }



    if (mx != ch) {

        cout << mx;

    }

    cout << ch << endl;

    return 0;

}