#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
const int N=(int)2000;
char c[N+2][N+2];
int p[N+2][N+2]={};
int ID[N+2][N+2]={};
int numrow,numcol;
int length,need_row;
vector<pair<int,int>>v;
void build_board(){
for(int i=1;i<=numrow;++i){
for(int j=numcol+1;j<=2*numcol;++j) {
c[i][j]=c[i][j-numcol];
}
}
for(int i=numrow+1;i<=2*numrow;++i){
for(int j=1;j<=numcol;++j) {
c[i][j]=c[i-numrow][j];
}
}
for(int i=numrow+1;i<=2*numrow;++i){
for(int j=numcol+1;j<=2*numcol;++j){
c[i][j]=c[i-numrow][j-numcol];
}
}
return;
}
class Hash_table{
public:
vector<int>h,p;
const int MOD=1e9+9;
const int base=9973;
void init(int _n){
h.assign(_n+2,0);
p.assign(_n+2,0);
}
void hash(int id){
p[0]=1;
for(int i=1;i<=numcol;++i){
p[i]=(LL)p[i-1]*base%MOD;
}
for(int i=1;i<=numcol;++i){
h[i]=((LL)h[i-1]*base+c[id][i]-'a'+1)%MOD;
}
}
int Get(int l,int r){
return ((LL)h[r]-(LL)h[l-1]*p[r-l+1]+(LL)MOD*MOD)%MOD;
}
};
Hash_table h[N+2];
//... COMPARE THE FUNCTION
bool cmp(pair<int,int>&x,pair<int,int>&y){
int low=1,high=length,p=0;
while (low<=high){
int mid=(low+high)/2;
if (h[x.first].Get(x.second,x.second+mid-1)==h[y.first].Get(y.second,y.second+mid-1)){
p=mid;
low=mid+1;
}
else high=mid-1;
}
if (p!=length) return c[x.first][x.second+p]<c[y.first][y.second+p];
if (x.first!=y.first) return x.first<y.first;
return x.second<y.second;
}
bool equal(pair<int,int>&x,pair<int,int>&y){
int low=1,high=length,p=0;
while (low<=high){
int mid=(low+high)/2;
if (h[x.first].Get(x.second,x.second+length-1)==h[y.first].Get(y.second,y.second+length-1)){
p=mid;
low=mid+1;
}
else high=mid-1;
}
return p==length;
}
bool check_possible(pair<int,int>&point,int x){
return point.first+(need_row-x)<=numrow;
}
int main(){
ios::sync_with_stdio(false);
cin.tie(0) ; cout.tie(0);
#define task "main"
if (fopen(task".inp","r")){
freopen(task".inp","r",stdin);
freopen(task".out","w",stdout);
}
cin>>numrow>>numcol;
for(int i=1;i<=numrow;++i){
for(int j=1;j<=numcol;++j){
cin>>c[i][j];
}
}
build_board();
numrow=2*numrow;
numcol=2*numcol;
length=numcol/2;
need_row=numrow/2;
for(int i=1;i<=numrow;++i) {
h[i].init(numcol);
h[i].hash(i);
for(int j=1;j<=numcol/2;++j) v.push_back({i,j});
};
sort(v.begin(),v.end(),cmp);
memset(p,0x3f,sizeof p);
int available=1;
int cnt=0;
vector<pair<int,int>>q;
for(int i=0,j=0;i<v.size();++i){
if (available==false) break;
while (j<v.size() && equal(v[i],v[j])) ++j;
bool ok=available;
++cnt;
for(int id=i;id<j;++id){
int x=v[id].first,y=v[id].second;
ID[x][y]=cnt;
if (check_possible(v[id],available) && available) q.push_back(v[id]),ok=false;
}
available=ok;
i=j-1;
}
pair<int,int>final={-1,-1};
for(int i=1;i<=need_row;++i){
vector<pair<int,int>>used;
bool ok=false;
for(auto&x:q) {
p[x.first][x.second]=i;
if (i==need_row){
final=x;
ok=true;
}
used.push_back({x.first+1,x.second});
}
if (ok) break;
sort(used.begin(),used.end(),[&](pair<int,int> x,pair<int,int> y){
return ID[x.first][x.second]<ID[y.first][y.second];
});
while (used.size()>1 && ID[used.back().first][used.back().second]!=ID[used.front().first][used.front().second]){
used.pop_back();
}
swap(q,used);
}
for(int i=1;i<=numrow;++i){
for(int j=1;j<=numcol;++j) if (p[i][j]==need_row) final={i,j};
}
assert(final.first!=-1 && final.second!=-1);
for(int i=final.first-need_row+1;i<=final.first;++i){
for(int j=final.second;j<=final.second+length-1;++j) cout<<c[i][j];
cout<<'\n';
}
}
