N = input()

#numbering = -1
smallest = 'Z' * 12

for loop in xrange(N):
    S = raw_input()
    #numbering = max(max(S), numbering)
    if len(S) == len(smallest):
        smallest = min(S, smallest)
    elif len(S) < len(smallest):
        smallest = S
    #print S, numbering, smallest

base = 36
while True:
    try:
        int(smallest, base)
        base -= 1
    except:
        base += 1
        print int(smallest, base)
        break