import sys
input=lambda:sys.stdin.readline().rstrip()
N,M=[int(input()) for i in range(2)]
A=[2,5]
for i in range(2):
	while M%A[i]==0:
		M//=A[i]
		N*=A[1-i]
while N%10==0:
	N//=10
print((N//M)%10 if N%M==0 else -1)