while True:
a = int(input())
if a == 0:
break
L = input().split()
for b in range(2,11):
try:
L2 = [int(i,b) for i in L]
except:
continue
else:
k = L2[1]-L2[0]
for j in range(2,len(L2)):
if k != L2[j] - L2[j-1]:
break
else:
print("Minimum base = {}.".format(b))
break
else:
print("No base <= 10 can be found.")