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

int N, i, shortest, min, j, k, cont, ok, delka;
char TMS[4000][201];
char ch;
char substr[201];

int main()
{
	while (1)
	{
		scanf("%d\n", &N);
		if (!N) return 0;
		shortest = 0;
		min = 300;
		for (i = 0; i < N; i++)
		{
			j = 0;
			while ( (ch = getchar()) > 30 )
			{
				TMS[i][j++] = ch;
			}
			if (j < min) { min = j; shortest = i; }
			TMS[i][j] = 0;
		}
		cont = 1;
		for (delka = min; delka > 0; delka--)
		for (i = 0; i + delka <= min && cont; i++)
		for (j = min; j >= i + delka && cont; j--)
		{
			strncpy(substr, &TMS[shortest][i], delka);
			substr[delka] = 0;
			ok = 1;
			for (k = 1; k < N && ok; k++)
				if (!strstr(&TMS[k][0], substr)) ok = 0;
			if (ok)
			{
				printf("%s\n", substr);
				cont = 0;
			}
		}
		if (cont) printf("IDENTITY LOST\n");
	}
}