#include <bits/stdc++.h>

using namespace std;

__int128 gcd(__int128 a, __int128 b)
{
	if (b == 0)
	{
		return a;
	}
	return gcd(b, a % b);
}

int main(void)
{
	cin.tie(0);
	ios::sync_with_stdio(false);
	
	unsigned long long int n, m;

	cin >> n >> m;
	__int128 N = n;
	__int128 M = m;
	__int128 g = gcd(N, M);
	N /= g;
	M /= g;
	
	__int128 temp = M;

	while (1)
	{
		if (temp % 2 != 0)
		{
			break;
		}
		temp /= 2;
	}
	while (1)
	{
		if (temp % 5 != 0)
		{
			break;
		}
		temp /= 5;
	}
	if (temp > 1)
	{
		cout << -1 << '\n';
		return 0;
	}
	

	int res = 0;
	__int128 XX = N / M;
	while (XX > 0)
	{
		if (XX % 10 != 0)
		{
			res = XX % 10;
			break;
		}
		XX /= 10;
	}
	N %= M;
	while (1)
	{
		if (N == 0)
		{
			break;
		}
		N *= 10;
		__int128 a = N / M;
		N %= M;
		//cout << N << ' ' << a << '\n';
		res = a;
	}
	cout << res << '\n';

	return 0;
}