// 2011アジア地区予選 B : The Sorcerer's Donut

#include <iostream>
#include <string>

using namespace std;

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

int main(){
	int h, w;
	string mp[10];
	while(cin >> h >> w, h){
		for(int i=0;i<h;i++) cin >> mp[i];
		string res = "";
		for(int i=0;i<w*h;i++){
			if(res.size() == w*h) break;
			int x1 = i/w, y1 = i%w;
			for(int j=i+1;j<w*h;j++){
				if(res.size() == w*h) break;
				int x2 = j/w, y2 = j%w;
				if(mp[x1][y1]!=mp[x2][y2]) continue;
				for(int di=0;di<8;di++){
					for(int dj=0;dj<8;dj++){
						string cur;
						int nx1 = (x1+dx[di]+h)%h, ny1 = (y1+dy[di]+w)%w;
						int nx2 = (x2+dx[dj]+h)%h, ny2 = (y2+dy[dj]+w)%w;
						if(mp[nx1][ny1]!=mp[nx2][ny2]) continue;
						cur += mp[x1][y1];
						while((x1 != nx1 || y1 != ny1) && (x2 != nx2 || y2 != ny2) && mp[nx1][ny1] == mp[nx2][ny2]){
							cur += mp[nx1][ny1];
							nx1 = (nx1+dx[di]+h)%h, ny1 = (ny1+dy[di]+w)%w;
							nx2 = (nx2+dx[dj]+h)%h, ny2 = (ny2+dy[dj]+w)%w;
						}
						if(cur.size() > res.size()) res = cur;
						else if(cur.size() == res.size()) res = min(res, cur);
					}
				}
			}
		}
		cout << (res=="" ? "0" : res) << endl;
	}
}