// yukicoder 25 (http://yukicoder.me/problems/70)
#include<cstdio>

typedef long long ll;

ll N, M;

ll gcd( ll a, ll b )
{ return b?gcd(b,a%b):a; }

int main()
{
	scanf( "%lld%lld", &N, &M );
	
	ll g = gcd( N, M );
	N /= g; M /= g;

	ll p2 = 0, p5 = 0;
	while( M % 2 == 0 )
		++p2, M>>=1;
	while( M % 5 == 0 )
		++p5, M/=5;

	if( M != 1 )
	{ puts("-1"); return 0; }

	while( N % 10 == 0 )
		N /= 10;

	while( p2 < p5 )
		++p2, N=(N<<1)%10;
	while( p2 > p5 )
		++p5, N=(N*5)%10;

	printf( "%lld\n", N%10 );

	return 0;
}