#include <bits/stdc++.h>
using namespace std;
#define all(c) (c).begin(),(c).end()
#define rrep(i,n) for(int i=(int)(n)-1;i>=0;i--)
#define REP(i,m,n) for(int i=(int)(m);i<(int)(n);i++)
#define rep(i,n) REP(i,0,n)
#define iter(c) __typeof((c).begin())
#define tr(it,c) for(iter(c) it=(c).begin();it!=(c).end();it++)
#define mem(a) memset(a,0,sizeof(a))
#define pd(a) printf("%.10f\n",a)
#define pb(a) push_back(a)
#define in(a) insert(a)
#define pi M_PI
#define R cin>>
#define F first
#define S second
#define C class
#define ll long long
#define ln cout<<'\n'
#define _(_1,_2,_3,N,...)N
#define pr(...) _(__VA_ARGS__,pr3,pr2,pr1)(__VA_ARGS__)
template<C T>void pr1(T a){cout<<a;ln;}
template<C T,C T2>void pr2(T a,T2 b){cout<<a<<' '<<b;ln;}
template<C T,C T2,C T3>void pr3(T a,T2 b,T3 c){cout<<a<<' '<<b<<' '<<c;ln;}
template<C T>void PR(T a,int n){rep(i,n){if(i)cout<<' ';cout<<a[i];}ln;}
bool check(int n,int m,int x,int y){return x>=0&&x<n&&y>=0&&y<m;}
const ll MAX=1000000007,MAXL=1LL<<60,dx[8]={-1,-1,-1,0,0,1,1,1},dy[8]={-1,0,1,-1,1,-1,0,1};
typedef pair<int,int> P;

void Main() {
  int n,m;
  while(cin >> n >> m && n) {
    string s[n];
    rep(i,n) R s[i];
    map<string,int> d;
    rep(i,n) {
      rep(j,m) {
        rep(k,8) {
          string t="";
          int x=i,y=j;
          while(1) {
            t+=s[x][y];
            d[t]++;
            x+=dx[k];
            y+=dy[k];
            if(x<0) x+=n;
            if(x>=n) x-=n;
            if(y<0) y+=m;
            if(y>=m) y-=m;
            if(x==i&&y==j) break;
          }
        }
      }
    }
    string ans="0";
    tr(it,d) {
      if(it->F.size()<=1 || it->S<2) continue;
      if(ans.size()<it->F.size()) ans=it->F;
      else if(ans.size()==it->F.size()) ans=min(ans,it->F);
    }
    pr(ans);
  }
}

int main() {
  ios::sync_with_stdio(0);cin.tie(0);
  Main();return 0;
}
