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

char input[4001][201];
char sablona[201];
int lengths[4001];

int main() {
  while (1) {
    int cases;
    int i, min_index;
    int lines = 0;
    int min_length = 201;
    scanf("%d\n", &cases);
    if (!cases) break;
    for (i = 0; i < cases; i++) {
      scanf("%s\n", input[lines]);
      int tmp = strlen(input[lines]);
      lengths[i] = tmp;
      if (min_length > tmp) {
	min_length = tmp;
	min_index = lines;
      }
      lines++;
    }
    int len = lengths[min_index];
    int offset = 0;
    int j;
    int max_match = 0;
    char string_match[201];
    for (i = len; i >= 0; i--) {
      for (offset = 0; offset < len-2; offset++) {
	strncpy(sablona, input[min_index]+offset, i);       
	int match = 0;
	for (j = 0; j < lines; j++) {
	  if (strstr(input[j], sablona)) {
	    match++;
	  } else {
	    break;
	  }
	}
	if(match == lines) {
	  if (len-offset > max_match || (len-offset == max_match && strcmp(string_match, sablona) > 0)) {
	    strcpy(string_match, sablona);
	    max_match = len-offset;
	  }
	}
      }
      if (max_match != 0) {
	break;
      }
    }
    if (max_match != 0) {
      printf("%s\n", string_match);
    } else {
      printf("IDENTITY LOST %s\n", input[i]);
    }
  }
  
  return 0;
}