#define  _CRT_SECURE_NO_WARNINGS
#pragma comment (linker, "/STACK:526000000")

#include "bits/stdc++.h"

using namespace std;
typedef string::const_iterator State;
#define eps 1e-11L
#define MAX_MOD 1000000007LL
#define GYAKU 500000004LL

#define MOD 998244353LL
#define seg_size 262144*2LL
#define pb push_back
#define mp make_pair
typedef long long ll;
#define REP(a,b) for(long long (a) = 0;(a) < (b);++(a))
#define ALL(x) (x).begin(),(x).end()

unsigned long xor128() {
	static unsigned long x = 123456789, y = 362436069, z = 521288629, w = time(NULL);
	unsigned long t = (x ^ (x << 11));
	x = y; y = z; z = w;
	return (w = (w ^ (w >> 19)) ^ (t ^ (t >> 8)));
}

void init() {
	iostream::sync_with_stdio(false);
	cout << fixed << setprecision(20);
}

#define int ll

void solve() {
	while (true) {
		int h, w;
		cin >> h >> w;
		if (h == 0) return;
		vector<string> inputs;
		REP(i, h) {
			string s;
			cin >> s;
			inputs.push_back(s);
		}
		map<string, int> cnter;
		REP(i, h) {
			REP(q, w) {
				int dx[3] = { 1,0,-1 };
				REP(j, 3) {
					REP(t, 3) {
						if (j == 1 && t == 1) continue;
						pair<int, int> now = mp(i, q);
						string s;
						while (true) {
							s.push_back(inputs[now.first][now.second]);
							now.first += dx[j];
							now.second += dx[t];
							now.first += h;
							now.second += w;
							now.first %= h;
							now.second %= w;
							cnter[s]++;
							if (now.first == i && now.second == q) break;
						}
					}
				}
			}
		}
		//cout << cnter["ABRACADABRA"] << endl;
		string ans = "0";
		for (auto x : cnter) {
			if (x.second >= 2) {
				if (ans.length() < x.first.length()) {
					ans = x.first;
				}
			}
		}
		cout << ans << endl;
	}
}

#undef int
int main() {
	init();
	solve();
}
