A, B, C = map(int, input().split(' '))
coin_num = A + B
total_money = A + 10 * B 
use_coins = A + B - C
if use_coins <= 0:
    print('impossible')
elif use_coins >= A:
    money_list = [(i + (use_coins - i) * 10) for i in range(use_coins)]
    print(sorted(money_list)[0])
elif use_coins <= A:
    money_list = [A - (i + (C - B - i) * 10)
                  for i in range(C - B) if A - (i + (C - B - i) * 10) > 0]
    print(sorted(money_list)[0])