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

int arithmetic(char s[5][6], int n, int b)
{
  int num[5], i;
  char *p;

  for (i = 0; i < n; i++) {
    num[i] = strtol(s[i], &p, b);
    if (*p) {
      return 0;
    }
  }

  for (i = 0; i < n-1; i++) {
    if (num[i+1] - num[i] != num[1] - num[0]) {
      return 0;
    }
  }
  return 1;
}

int main(void)
{
  int n, i, found;
  char s[5][6];
  while (scanf("%d", &n) == 1 && n > 0) {
    for (i = 0; i < n; i++) {
      scanf("%s", s[i]);
    }

    found = 0;
    for (i = 2; i <= 10 && !found; i++) { 
      if (arithmetic(s, n, i)) {
	printf("Minimum base = %d.\n", i);
	found = 1;
      }
    }
    if (!found) {
      printf("No base <= 10 can be found.\n");
    }
  }
  return 0;
}