A, B, C = map(int, input().split())

n = A + B - C 
if n > 0:
    if n <= 10 and A >= n:
        print(n)
    elif n <= 10 and A <n:
        print(A+10*(n-A))
    elif n > 10 :
        n1 = n + n//10
        if n1 <= A:
            n2 = n1 - n1//10*10
            print(n2)
        else:
            n_10 = n - A
            print(A + n_10*B)                    
elif n < 0:
    print(10 + n -1)    
else:
    print("impossible")