N = raw_input()
M = raw_input()

if M == '1':
    print filter(lambda c:c!='0', N)[-1]
    exit()
if any(c=='0' for c in format(int(M)-1, 'b')) and M[-1] not in '05':
    print -1
    exit()

A = 0
i = 0
M = int(M)
while True:
    if i < len(N):
        A = A*10 + int(N[i])
    else:
        A *= 10
    C, A = A/M, A%M
    if C != 0:
        B = C
    if (A == 0) and i >= len(N)-1:
        print B
        break
    i += 1