#include <iostream>
#include <string>
#include <utility>
#include <algorithm>
#include <map>
#include <set>
#include <vector>
#include <cmath>
#include <cstdlib>
#include <queue>
#include <stack>
#include <iomanip>

using namespace std;

#define REP(i, n) for(ll i = 0;i < n;i++)
#define REPR(i, n) for(ll i = n;i >= 0;i--)
#define FOR(i, m, n) for(ll i = m;i < n;i++)
#define FORR(i, m, n) for(ll i = m;i >= n;i--)
#define REPO(i, n) for(ll i = 1;i <= n;i++)
#define ll long long
#define INF (ll)1 << 60
#define MINF (-1 * INF)
#define ALL(n) n.begin(),n.end()
#define MOD 1000000007
#define P pair<ll, ll>

ll n, m, mm, ans, no;

ll gcd(ll a, ll b) {
	return (b == 0 ? a : gcd(b, a % b));
}
int main() {
	cin >> n >> m;
	mm = m;
	if (n % m == 0) {
		ll now = n / m;
		while (1) {
			if (now % 10 != 0) {
				cout << now % 10 << endl;
				return 0;
			}
			now /= 10;
		}
	}
	ll g = gcd(n, m);
	n /= g;
	m /= g;
	while (mm % 2 == 0)mm /= 2;
	while (mm % 5 == 0)mm /= 5;
	if (mm != 1) {
		cout << -1 << endl;
		return 0;
	}
	
	double a = (double)n / m;
	
	REP(i,19) {
		if((ll)a % 10 != 0) ans = (ll)a % 10;
			no = (ll)a % 10;
		a *= 10;
		a -= no * 10;
	}
	cout << ans << endl;
}