3450

/*
KMP来做532ms
*/// include file
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <cctype>
#include <ctime>#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <bitset>
#include <strstream>#include <algorithm>
#include <string>
#include <vector>
#include <queue>
#include <set>
#include <list>
#include <functional>using namespace std;// typedef
typedef long long LL;
typedef unsigned long long ULL;// 
#define read freopen("in.txt","r",stdin)
#define write freopen("out.txt","w",stdout)
#define FORi(a,b,c) for(int i=(a);i<(b);i+=c)
#define FORj(a,b,c) for(int j=(a);j<(b);j+=c)
#define FORk(a,b,c) for(int k=(a);k<(b);k+=c)
#define FORp(a,b,c) for(int p=(a);p<(b);p+=c)#define FF(i,a)    for(int i=0;i<(a);i+++)
#define FFD(i,a)   for(int i=(a)-1;i>=0;i--)
#define Z(a) (a<<1)
#define Y(a) (a>>1)const double eps = 1e-6;
const double INFf = 1e10;
const int INFi = 1000000000;
const double Pi = acos(-1.0);template<class T> inline T sqr(T a){return a*a;}
template<class T> inline T TMAX(T x,T y)
{if(x>y) return x;return y;
}
template<class T> inline T TMIN(T x,T y)
{if(x<y) return x;return y;
}
template<class T> inline void SWAP(T &x,T &y)
{T t = x;x = y;y = t;
}
template<class T> inline T MMAX(T x,T y,T z)
{return TMAX(TMAX(x,y),z);
}// code begin
#define MAXN 4001
#define MAXM 202char dc[MAXN][MAXM];
int Len[MAXN];
int N;
int mins;
int minst;char P[MAXM];
int Ps;
int Ts;
int next[MAXM];char ans[MAXM];void CalNext()
{next[0] = 0;next[1] = 0;int j;FORi(2,Ps+1,1){j = next[i-1];while(true){if(P[j]==P[i-1]){next[i] = j+1;break;}if(j==0){next[i] = 0;break;}j = next[j];}}
}bool KMP(int cur)
{Ts = Len[cur];int i=0;int j=0;while(true){if(j==Ts) break;if(P[i]==dc[cur][j]){i++;j++;if(i==Ps){return true;}}else if(i>0){i=next[i];}elsej++;}return false;
}bool Isok()
{FORi(0,N,1){if(i!=mins){if(!KMP(i)){return false;}}}return true;
}int main()
{read;write;while(scanf("%d",&N)!=-1){if(N==0) break;minst = MAXM;FORi(0,N,1){scanf("%s",dc[i]);Len[i] = strlen(dc[i]);if(Len[i]<minst){minst = Len[i];mins = i;}}//找到了最短的子串 mins;for(int i=0;i<MAXM;i++)ans[i] = 'z';ans[MAXM] = 0;bool f=false;for(int len=Len[mins];len>0;len--){Ps = len;for(int i=0;i+len<=Len[mins];i++){strncpy(P,dc[mins]+i,len);P[len] = 0;CalNext();//然后和其余的串比较if(Isok()){if(strcmp(P,ans)<0){strcpy(ans,P);f=true;}}}if(f) break;}if(f) printf("%s\n",ans);else printf("IDENTITY LOST\n");}return 0;
}