#include<cstdio>


using ll=long long;
using ull=unsigned long long;


ull gcd(ull a, ull b)
{
	ull c;
	while((c=a%b))
	{
		a=b;
		b=c;
	}
	return b;
}


void com_div(ull& a, ull& b)
{
	ull d=gcd(a, b);
	a/=d;
	b/=d;
}


int main(void)
{
	ull n, m, t;
	int c2, c5;

	while(scanf("%llu%llu", &n, &m)==2)
	{
		com_div(n, m);

		t=m;
		for(c2=0;t%2==0;t/=2) c2++;
		for(c5=0;t%5==0;t/=5) c5++;

		if(t!=1)
		{
			printf("-1\n");
			continue;
		}
		if(c2>c5)
		{
			printf("5\n");
			continue;
		}

		for(;n%10==0;n/=10);
		n%=10;
		for(int i=c5-c2;i>0;i--) n=(n*2)%10;

		printf("%d\n", (int)n);
	}

	return 0;
}