#include<cstdio>

 #include<cstring>

 #define F(i,a,b) for(int i=a;i<=b;i++)

 const int N=;

 int nxt[N],n,lens[],ans,l,r,cnt;

 char dt[][N];

 int KMP(int n,char*a,int m,char*b){

     int i,j;

     for(nxt[]=j=-,i=;i<n;nxt[i++]=j){

         while(~j&&a[j+]!=a[i])j=nxt[j];

         if(a[j+]==a[i])j++;

     }

     for(j=-,i=;i<m;i++){

         while(~j&&a[j+]!=b[i])j=nxt[j];

         if(a[j+]==b[i])j++;

         if(j==n-)return ;

     }

     return ;

 }

 inline void up(int &a,int b){if(a<b)a=b;}

 inline void update(int L,int R){

     if(R-L+>ans)l=L,r=R,ans=r-l+;

     else if(R-L+==ans)

     {

         for(int i=l,j=L;;i++,j++){

             if(dt[][i]!=dt[][j]){

                 if(dt[][i]<dt[][j])return;

                 else{

                     l=L,r=R;

                     return;

                 }

             }

             if(i==r)return;

             if(j==R)l=L,r=R;

         }

     }

 }

 int main(){

     while(~scanf("%d",&n),n)

     {

         F(i,,n)scanf("%s",dt[i]),lens[i]=strlen(dt[i]);

         char tp[];

         ans=-,l=,r=,cnt=;

         F(i,,lens[]-)F(j,i+cnt,lens[]-)

         {

             int ed=,fg=;

             F(ii,i,j)tp[ed++]=dt[][ii];

             F(ii,,n)if(KMP(j-i+,tp,lens[ii],dt[ii])==){fg=;break;}

             if(fg)update(i,j),cnt=ans<?:ans-;//剪枝，每次只找大于ans的

         }

         if(ans==-)puts("IDENTITY LOST");

         else {F(i,l,r)printf("%c",dt[][i]);puts("");}

     }

     return ;

 }