#include <algorithm>
#include <cmath>
#include <climits>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <fstream>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <cassert>
#include <functional>

using namespace std;

#define LOG(...) printf(__VA_ARGS__)
//#define LOG(...)
#define FOR(i,a,b) for(int i=(int)(a);i<(int)(b);++i)
#define REP(i,n) for(int i=0;i<(int)(n);++i)
#define ALL(a) (a).begin(),(a).end()
#define RALL(a) (a).rbegin(),(a).rend()
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())
#define RSORT(c) sort((c).rbegin(),(c).rend())
#define CLR(a) memset((a), 0 ,sizeof(a))

typedef long long ll;
typedef unsigned long long ull;
typedef vector<bool> vb;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<vb> vvb;
typedef vector<vi> vvi;
typedef vector<vll> vvll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

const int dx[] = { -1, 0, 1, 0 }; const int dy[] = { 0, 1, 0, -1 };
const int dx8[] = { -1, -1, 0, 1, 1, 1, 0, -1 }; const int dy8[] = { 0, 1, 1, 1, 0, -1, -1, -1 };


int main() {
	int n, m;
	while (cin >> n >> m, n){
		int ma = 2;
		vector<string> code(n);
		vector<string> spell;
		set<string> ss;
		REP(i, n){
			cin >> code[i];
		}
		REP(i, n){
			REP(j, m){
				REP(k, 8){
					string s = "";
					int y=i;
					int x=j;
					while (1){
						s += code[y][x];
						if (s.length() >= ma){
							if (ss.find(s) == ss.end()){
								ss.insert(s);
							}else{
								if (ma < s.length()){
									ma = s.length();
									spell.clear();
								}
								spell.push_back(s);
								}
						}
						y += dy8[k]+n;
						y%=n;
						x +=dx8[k]+m;
						x%=m;
						if (y==i&&x==j)break;
					}
				}
			}
		}
		
		
		if (spell.empty())
			cout << "0"<<endl;
		else{
			SORT(spell);
			cout << spell[0] << endl;
		}
	}
}