#include <stdio.h>
#include <string.h>

int main()
{
	int n,i,zac,kon;
	char s[4000][201];
	int leng[201];
	int min;
	int minpocet;
	
	char sub[201];
	char najdene[201];
	
	int ok;
	
	while (scanf("%d",&n),n!=0)
	{
		strcpy(najdene,"");
		for (i=0;i<n;i++)
		{
			strcpy(s[i],"");
			scanf("%s",s[i]);
			leng[i]=strlen(s[i]);
			if (i==0)
			{
				min=0;
				minpocet=leng[i];
			}
			else
			if (leng[i]<minpocet)
			{
				min=i;
				minpocet=leng[i];
			}
		}
		for (zac=0;zac<minpocet;zac++)
		{
			for (kon=zac;kon<minpocet;kon++)
			{
				for (i=zac;i<=kon;i++)
				{
					sub[i-zac]=s[min][i];
				}

				sub[kon-zac+1]='\0';
				
				ok=1;
				
				for (i=0;i<n;i++)
				{
					if (strstr(s[i],sub)==NULL)
					{
						ok=0;
						break;
					}
				}
				
				if (ok==1)
				{
					if (strcmp(najdene,"")==0)
					{
						strcpy(najdene,sub);
					}
					else
					if (strlen(sub)>strlen(najdene))
					{
						strcpy(najdene,sub);
					}
					else
					if (strlen(sub)==strlen(najdene)&&strcmp(sub,najdene)<0)
					{
						strcpy(najdene,sub);
					}
				}
			}
		}
		if (strcmp(najdene,"")==0) 
			printf("IDENTITY LOST\n");
		else
			printf("%s\n",najdene);
		
		
	}
	
	
	return 0;
}