#include <stdio.h>
#include <cstdio>
#include <iostream>
#include <stdlib.h>
#include <string.h>
#include <vector>
#include <string>

#define TRADEMARKS 4000
#define STRLEN 200
using namespace std;

vector<string> pole;
vector<string> common;

int trademarks;

int min1, min1pos, min2, min2pos;

bool unique(string substring)
{
	vector<string>::iterator iter;
	for (iter = common.begin(); iter != common.end(); iter++)
	{
		if ((*iter).compare(substring) == 0)
		{
			return false;
		}
	}
	return true;
}
void solve()
{
	min1 = pole[min1pos].length();
	min2 = pole[min2pos].length();

	for (int len = min1; len > 0; len--)
	{
		for (int x = 0; x <= min1 - len; x++)
		{
			string substring;
			substring = pole[min1pos].substr(x, len);
			if (pole[min2pos].find(substring) != string::npos)
			{
				if (unique(substring))
				{
					common.push_back(substring);
				}
			}
		}
	}

	unsigned int index = 0;

	while ((index < common.size()) )
	{
		unsigned int tr = 0;
		bool deleted = false;
		while ((tr < pole.size())&& (common.size() > 0))
		{
			if (pole[tr].find(common[index]) == string::npos)
			{
				common.erase(common.begin() + index);
				deleted = true;
			}
			tr++;
		}
		if (!deleted)
			index++;
	}

	string min = "";


	for (unsigned int i = 0; i < common.size(); i++)
	{
		if (common[i].length() > min.length())
		{
			min = common[i];
		}
		else
		{
			if (common[i].length() == min.length())
			{
				if (min.compare(common[i]) > 0)
				{
					min = common[i];
				}
			}
		}
	}

	if (common.size() == 0)
	{
		cout << "IDENTITY LOST" << endl;
	}
	else
	{
		cout << min << endl;
	}
}

int main(void)
{
	scanf("%d", &trademarks);

	while (trademarks > 0)
	{
		pole.clear();
		common.clear();

		string a;
		int len;
		for (int i = 0; i < trademarks; i++)
		{
			cin >> a;
			pole.push_back(a);
			len = a.length();

			min1pos = 0;
			min2pos = 0;
			min1 = 201;
			min2 = 201;

			if ( (len < min1))
			{
				min2 = min1;
				min2pos = min1pos;
				min1pos = i;
				min1 = len;
			}
			else if (len <= min2)
			{
				min2pos = i;
				min2 = len;
			}
		}

		solve();

		scanf("%d", &trademarks);
	}

	return 0;
}